The Cross Creek Hypothesis

I would like to describe a land form that I have noticed but cannot find documented anywhere. Simple logic dictates that when there is a gradual slope to underlying rock strata, a flow of water on the land above will flow along the slope of the rock strata and thus the land. However, there are a number of creeks (brooks or streams) in areas that were once covered by glaciers that flow not along the direction of slope to the land but across it.

In the Niagara Falls, NY area, there are two such examples of "cross creeks", as I will call them. Here is a map link with satellite imagery if you want to have a look http://www.maps.google.com/

One is Bergholz Creek in Niagara County, within the city limits of Niagara Falls, it is known as Black Creek. From Lockport Road, it is easy to see the southward slope of the land while looking across the farms to the Village of Bergholz. So why then does Bergholz Creek flow more westward, rather than southward?

Ellicott Creek in nearby Tonawanda also follows exactly the same pattern. We can see that south of the creek in the City of Tonawanda the ground is actually subtly sloping downward going south away from the creek. At first glance, this seems to make no sense. Why does the creek flow westward while the slope of the land is primarily southward?

To explain the flow of these two creeks, let me now describe the formation of a cross creek. At the end of the last ice age, about 12,000 years ago, the glacier began to melt and break apart as the climate became warmer. In places where there was some slope to the land, as in the Niagara Falls area, massive bergs of ice slid across the slope of the underlying rock strata, plowing up the ground in front of them until they melted enough to come to a halt.

At the edge of the melting berg, a flow forms from the meltwater but because of the furrow in the ground that the berg has plowed, the water flows across, rather than along, the primary slope of the land and a cross creek is born. A cross creek usually joins a larger creek that is not a cross creek.

In Niagara Falls, neither Cayuga Creek, which Bergholz Creek joins, nor Gill Creek are cross creeks. I decided not to classify Tonawanda Creek as a cross creek because I believe it to have been the primary drainage channel of the eastward portions of the fomer Lake Tonawanda that covered much of the area after the end of the last ice age.

Cross creeks require sliding bergs of ice to form and may have acquired seemingly illogical bends or turns. Both Bergholz and Ellicott Creeks make northward bends, against the underlying slope of the land, before joining larger creeks.

The Next Ice Age

There have been more than twenty known ice ages in the history of our planet and much has been written about their effects that we can see today. But have you ever wondered what changes to the present geography of earth the next ice age will bring? To explore this question we must, of course, put global warming aside for the moment and assume that there will be another ice age in the future.

Basically, the continents and islands of the world are built up by tectonic collisions and volcanic activity which is then shaped by primary and secondary glaciation during the ice ages. A glacier that advances southward during ice ages is a mountain of ice maybe two km thick that spans an area hundreds of kilometers wide. As I have pointed out in my discussions of glaciation, much of the lasting effect on the landscape of glaciers is from secondary, rather than primary, glaciation. That is at the end of ice ages as the climate warms, massive bergs of ice break off the melting glacier and impact and slide over the land below.

It is my feeling that the place which will be most affected by the next ice age will be Europe. On http://www.maps.google.com/ we can see the vast shallow area of water around northwestern Europe. It is also easy to see how the continents have split apart due to the volcanic spreading of the Mid-Atlantic Ridge. This vast wedge-shaped area of shallow water can be seen to have split off the area of continental shelf around Newfoundland in eastern Canada.

This area of shallow water in northwestern Europe was almost certainly once all land which has been eroded away to below the water level by glaciers in successive ice ages. This includes the North, Baltic and, Irish Seas also the English Channel and far out into the Atlantic Ocean. You can see a shallow area to the northwest of Ireland and about the size of that country. This must have once been an island about the size of Ireland that is now gone. Denmark is all lowland that would have been eroded away by glaciers except that it was shielded by the bulk of the Norwegian Mountains.

There are two significant curves that we can see on the map of western Europe where glaciers have carved away at the land in ice age after ice age. the west coast of France along the Bay of Biscay has been gradually carved away although it has been shielded by the mountains on the peninsula known as Brittany. The other curve is from the northwest corner of the Netherlands to Calais at the Strait of Dover. We can expect that the next ice age will continue this process.

In my posting, "New Discoveries In Northern Europe" on this blog, I explained why Britain must have had ice crossing it from both the northwest, where it would usually come from, and also the northeast, due to ice piling up against and being deflected by the Norwegian Mountains. The ice from the northwest should be far greater in volume but it actually is not, because Britain is in the "glacial shadow" of Iceland.

The main route across England of the ice that comes from the northwest during ice ages is through the North Channel, which separates Scotland from Northern Ireland. The main route of ice then follows what I will call the "Severn Route". There is are two bays just southwest of Liverpool with Birkenhead between them. This represents the crossing of the main bulk of glacial ice onto land from the shallow sea, which freezes during the ice ages.

The ice goes around the Welsh mountains and is diverted southward by the southern portion of the Pennine Mountains. The ice continues southward through what is now called the "Severn Vale" and is occupied by the present-day Severn River. The flow of ice continues to the Bristol Channel.

The mountains of Wales are the primary factor preventing the ice from taking a more direct route southward. The Severn Vale is much too vast to have been carved by water alone and there is no evidence that it is a fissure in the earth's crust or anything like that. Furthermore, I have shown in my posting "New Discoveries In The Forest Of Dean" on this blog that the ice from the Vale produced a glacial impact crater at Cinderford.

My hypothesis is that the Severn Vale has not yet been eroded enough by the ice in ice ages to be below water but that may well change with the next ice age. Wales will become an island at that time and there will be a channel of the sea from what is now Liverpool to Bristol.

The only reason that this has not yet happened, that the Severn Vale is still dry land is the Isle of Man. The main thrust of the glacial ice comes through the break in the mountains and high ground that is the North Channel. But instead of going straight toward Liverpool, the majority of the ice is diverted southward by the mountainous Isle of Man.

Only a portion of the main glacial thrust goes around the Isle to the north and goes through the Severn Route. Liverpool and the Severn Vale are in the glacial shadow of the Isle of Man just as all of Britain is in the glacial shadow of Iceland.

The Isle of Man itself is being eroded away by glaciation in successive ice ages. When it is gone, the main thrust of ice will go through what then may be called the "Severn Channel" and it will get wider and wider. Eventually Wales, as seen from England, will be but a line of mountains on the horizon.

The Carmarthen Raceway

I notice that there is a valley in south Wales that has had a very important role in shaping the coastal topography of the southwestern part of the country. I did a survey of the landscape of Wales using http://www.maps.google.com/ as well as the more advanced Google Earth, which is not free on the internet. This valley extends from the town of Carmarthen northeastward to Builth Wells. In surveying the valley using Google Earth, I started in Builth Wells and found my way to Carmarthen by following the area on the screen lowest in elevation above sea level.

The great effect that this valley must have had on the Welsh coast centers around what happens at the end of each of the successive ice ages. As the climate gets warmer, the glacial ice in the warmer lowlands will melt first. As the ice in the mountains begins to melt and break apart into large bergs, it slides along valleys such as this, which I have termed "The Carmarthen Raceway", on the way to the sea. As it does, it reshapes the coastline.

Ice usually covers about 10% of the earth's surface but during ice ages, that increases to maybe 30%. There is known to have been more than twenty such ice ages.

(Note to readers- In this posting I have attempted, as far as is possible, to select landmarks that have English, rather than Welsh, names. Cities tend to have English names but many towns and villages in Wales have Welsh names. This is not intended as an affront to Wales, which is a fabulous and scenic place, but only for the ease of my readers. Welsh names are not pronounced as they appear in English and three Welsh letters are not used in the English language and are written in Welsh as doubles- FF, LL and, DD.)

Carmarthen Bay on the south coast of Wales was dug by ice moving through the Carmarthen Raceway at the end of each ice age. Using the satellite imagery on http://www.maps.google.com/ you can easily see how cliffs alternate with beach around the coast of Carmarthen Bay, the shadows of the cliffs can be seen. This is because, ice from the Raceway will carve away the cliffs to form a low area and then moving ice from successive ice ages will follow the same low path. This leaves cliffs intact in some places but erases the cliffs to form beach in others.

Notice how there is much more sand, including the vast Pendine Sands, on the eastern side of Carmarthen Bay. This is simply because of the northeastward direction of the waves from the ocean.

There is much more cliff that has survived the ice ages around Saundersfoot on the western shore of the bay because that was more in line with the direction from which ice came from the Carmarthen Raceway. At the holiday town of Tenby, at the southwestern corner of Carmarthen Bay, there is an extensive stretch of beach facing east but a short distance away, there is no beach facing south. This plainly illustrates how the moving ice removes cliffs to form beaches and the direction of the Carmarthen Raceway from which it came.

Notice the two small islands just off Tenby that are islands at high tide but not at low tide. It is obvious that these satellite images were taken at low tide because many small boats can be seen on the sand at Saundersfoot and Tenby.

From high up, you can see that there are two long stretches of wide beach that are parallel to each other, along the same axis. One is at Tenby and the other is from Saundersfoot to Amroth. These point along the main direction of the moving ice and point directly at the Carmarthen Raceway.

Caldey Island, the large island south of Tenby, was cut away from the mainland by the ice over successive ice ages. From above, it is easy to see how the island is gradually being cut up by the ice. The buildings on the island are a Cistercian monastery. (I believe it is also spelled "Caldy" but on the map it is mispelled "Caldney")

I notice many of what I will call "gorges" on the southwestern coast of Wales. I call them this because they remind me of miniature versions of the one at Niagara Falls. There are three of them in a row on the coast south of Buckspool, west of Tenby. I am certain that these gorges are the first step in the destruction of a stretch of cliff to form a beach. Gorges are narrow while beaches are wide. They are most likely formed by flowing meltwater from glaciers that forms a waterfall over the cliff and erodes it's way backward.

Moving westward, the city of Milford Haven lies in a low area near the coast with a river. This is actually the deepest waterway in Europe and was obviously carved out by moving ice. Remember that bodies of water dug by glaciers tend to be either broad and shallow or narrow and deep.

The form of the coast around the inlet to Milford Haven is similar to that of southwest Ireland and was formed in the same way. It is easy to see the path of the ice here at Sandy Haven, west of Milford Haven, and by the extensive beach at Castlemartin nearby.

In my estimation, there are three main tracks that the ice from the Carmarthen Raceway follows on it's way to the sea at the end of each ice age. The first is that which formed Carmarthen Bay. The second is that which dug the waterway at Milford Haven. The third is the one which created St. Bride's Bay to the north of Milford Haven.

At the southwestern corner of St. Bride's Bay there is very rugged rock that has resisted the ice while being "polished" by it. You can see how Skomer and Skokholm Islands were cut away from the mainland by the ice, just as Caldey Island was. Notice how the southward shore of Skomer Island is much more rugged than it's northern shore because this is the direction in which the ice was moving.

The thing that is so interesting about St. Bride's Bay is that wide beaches are to be found only on it's eastern shore because this is the direction from which the ice came. The eastern shore, in sharp contrast to the other shores, is more beach than cliff. There are relatively few cliffs there, such as the one at Broadhaven.

Another point of interest concerning St. Bride's Bay is that there are many narrow gorges on it's northern shore but none on it's southern shore. The ones on the northern shore all point to the southwest, the direction in which the ice was moving from the Carmarthen Raceway.

Waves from the ocean are certainly also a factor in the erosion and shaping of coastlines such as this, but by far the main factor was this ice. There are many videos on http://www.youtube.com/ of this area of the Pembrokeshire coast so you can see up close what it looks like.

In my survey of the Welsh coast, I notice that the west coast of Wales gets smoother as we go north. This is because it was away from the ice flow of the Carmarthen Raceway. The coast gets noticably smoother north of New Quay and smoother still north of Aberystwyth (This is the Welsh name of Wales' most important west coast city but English people say it the way it looks in English, although this pronounciation is not technically correct.) However, north of Caernarvon Bay to Holyhead the coast becomes rugged again. Anglesey clearly displays the southwest to northeast lines of primary glacial movement from beyond the shield provided by the mountains of Wales.

Going back to south Wales, you will notice another bay to the west of Carmarthen Bay by the name of Swansea Bay near the city of that name. This bay was formed in exactly the same way as Carmarthen and St. Brides Bays. There is a valley northward from this bay up to Brecon Beacons through which flows the Neath River. This valley operated as a raceway for the ice in the same way as the Carmarthen Raceway.

Far to the north on the west coast of England is the large Morecambe Bay. This was also formed by bergs of ice at the end of ice ages flowing through a nearby valley after coming down from mountains. In surveying Morecambe Bay by the satellite imagery, it does not seem to have the cliffs around it that the Welsh bays do and this made the erosion faster and more extensive to form a larger bay.

On the far western tip of France we find the same type of phenomenon. I did a survey of this area and there is the same alternation of cliffs and beaches. Notice that Baie de Douamenez and the nearby waterway at the city of Brest is very similar to St. Brides Bay and the nearby waterway at Milford Haven. The main difference is that in Wales, the bay is to the north of the glacial waterway while in France it is to the south.

The Story Of The Forest Of Dean Area

There have been two parts to the posting "New Discoveries In The Forest Of Dean". Recently, I became aware of a project to extensively photograph every corner of Britain and Ireland and post the tens of thousands of photos. The site of this project is http://www.geograph.org.uk/. I have found the photos on the site to be immeasurably helpful in the study of natural history and I have decided to supplant the previous postings with this one, with links to photos included.

Here are map links. If you wish to follow along on a map, just enter in Lydbrook to start. http://www.maps.google.com/ and http://www.multimap.com/ The Forest of Dean is the western portion of Gloucestershire in England, along the border with Wales. Much of what we will be discussing is in the neighboring county of Herefordshire.

By the way, both of these map sites offer a download to make the map three-dimensional and I would like to assure readers that both downloads are perfectly safe.

I am so interested in the Forest of Dean simply because Lydbrook was where I entered the world. In terms of physical geography, the northern section of the forest is high ground divided up by several valleys. The hills representing the high ground are not material deposited by glaciers. Rather, the layers of rock representing the high ground are being cut up by glacial movement during the ice ages, leaving the valleys.

The high ground in the Forest of Dean could well have been land forced upward during the continental collision that I described in the posting "The Mysterious Geography Of Britain" earlier in this blog.

The wonderful thing about these photos is that they enable all readers, even the vast majority which would not be familiar with this area, to see how glaciers interact with land during ice ages. Similar examples can be found all over the approximately 30% of the world that was then covered by glaciers. The activity of glaciers in the Forest of Dean involves both primary glaciation, the movement of glaciers at the beginning of ice ages and secondary glaciation, the effects on the land when glaciers melt and break up at the end of an ice age.

There have been more than twenty ice ages. The last one began about 20,000 years ago and ended about 12,000 years ago.

SYMONDS YAT

Let's start our exploration of the Forest of Dean at a place called Symonds Yat. There are two slices into the rocky high ground here, which were created by the glaciers coming down from the Welsh Mountains during the ice ages. The glaciers which passed over the forest probably originated in the low area northwest of the city of Hereford, around Weobley and Kington, which is sorrounded on three sides by mountains. As I have documented on my geology blog, http://www.markmeekearth.blogspot.com/ glacial ice actually moves toward the southeast, rather than due south, because the eastward rotation of the earth imparts momentum to it.

It is very important to realize that it was not the main force of the glaciers which passed over the forest during the ice ages, but the somewhat lesser glaciers which came down out of the mountains. If it had been the main force of the glacier it is possible that all of the high ground in the Forest of Dean would be gone by now, but the Welsh Mountains formed a shield.

The main thrust of the glaciers from the northwest went between the gap between the Welsh Mountains and the Pennines at Liverpool. The glaciers carved away the ground as they proceeded along this route and the result is the Severn Vale. This is the broad low area around the Severn River. The Forest of Dean is on one side of the Severn Vale. The ice which passed over the forest joined the main flow of ice here.

Overlooking the village of Symonds Yat is the observation point on Yat Rock. If we look northwest from there, this is what we see:

www.geograph.org.uk/photo/784049
www.geograph.org.uk/photo/1117516

Notice the Welsh Mountains in the distance, and the lowland in between. This is from where the glaciers came www.geograph.org.uk/photo/530746

We are looking northwest in these photos. The valley is the Wye Valley, named for the river which flows through it. The Wye flows southward from here and joins the Severn River at Chepstow.

In no way did this river carve the valleys through which it flows, the glaciers carved the valleys and the flow of the river found it's way through after the last ice age. The large loop in the Wye River on opposite sides of Yat Rock through Huntsham demonstrate how fast the water must have been flowing at the end of the ice age. It required this wide loop to make the 180 degree change of direction.

The formation of valleys like these through layers of rock do not necessarily happen during one ice age. A flow of water, whether from a permanent river or a flow of meltwater at the end of an ice age, will weaken the rock beneath it. Then when the next ice age arrives, the ice can push it's way into the weakened rock and the process is repeated over successive ice ages, until we have the finished valley.

Now let's look in the other direction from the top of Yat Rock, to the northeast: www.geograph.org.uk/photo/1617787

The elongated hill on the right is known as Coppet Hill (I have seen it spelled in different ways). Coppet Hill is aligned at a moderate angle to the direction of glacial movement from the northwest. The result is that it deflected the oncoming ice so that it broke through the limestone to the east side (right) of Yat Rock.

The elongated Coppet Hill also acted as a barrier so that it created a "glacial vacuum" behind it. Further east, the ice broke through the rock at yet another point at Kerne Bridge. The ice that came through there was diverted by the ice piled up against Ruardean Hill so that it was diverted into the "glacial vacuum" behind Coppet Hill.

This movement of ice eventually met that which had cut into the rock at the east side of Yat Rock. The result as seen today is the semi-circular valley around Coppet Hill and the area to the east of it, up to Kerne Bridge.

Here is the view, looking north, from the top of Coppet Hill. You can see the Kerne Bridge, over the Wye River, and Leys Hill on the other side of it. After Leys Hill, there is Chase Hill. The valley between Leys Hill and Chase Hill is at Coughton, which we will get to later. On the other side of Chase Hill is the town of Ross-on-Wye, which also has a valley that we will see. www.geograph.org.uk/photo/1187565

Here is a view of Coppet Hill from Leys Hill, to the east. The valley and the Wye River is between the hills: www.geograph.org.uk/photo/1309557

In this view, the mountains from where the glaciers came are in the distance. Coppet Hill is closer and the Wye River is in a hidden valley, carved by the glacier, before Coppet Hill: www.geograph.org.uk/photo/119223

Here is a view of the mountains in the distance from Ruardean, on Ruardean Hill south of Leys Hill: www.geograph.org.uk/photo/119217 A lot of glacial ice was pressed against Ruardean Hill during ice ages and when it melted, it formed Lodgegrove Brook, which runs east-west just north of Ruardean Hill.

LYDBROOK

Now, let's consider the long valley which extends southward from the village of Lydbrook. In fact, Lydbrook is built along the road along the bottom of the valley.

The two channels of ice described above, one beginning to the east of Yat Rock and the other beginning at Kerne Bridge, cutting their way through the rock, met at what is now the bottom of Lydbrook, where the Wye River now flows. The two channels of ice collided and diverted one another southward, cutting the valley through Lydbrook.

The peaceful serenity of Lydbrook along the Wye today belies the violence of the ice collision which formed it, the same goes for Symonds Yat. If you wonder how moving ice can cut such relatively neat channels through rock the reason, once again, is that a flow of water in times past will weaken the rock so that moving ice during a subsequent ice age will find the weak spots in the rock and force it's way through.

The valley through Lydbrook is dry today, but at the end of the ice ages it was a raging river of water from the melting glacier atop the area. It extends along New Road through Parkend and onward to the Severn. There are a number of entrances through which meltwater flowed into the Lydbrook Valley which are readily visible today. One is the valley around Speech House Road just east of Mile End and Broadwell, near Coleford. Deeper in the forest, water running into the Lydbrook Valley long ago formed a canyon at Wimberry Slade. There are more such channels to be seen on an ordnance map of the forest.

Here is where this great collision of ice took place at the bottom of Lydbrook, where the Wye River flows today: www.geograph.org.uk/photo/523362

This is another view of the Wye Valley, where the collision took place: www.geograph.org.uk/photo/1427622

These are views across the valley through Lydbrook. These are closest to the Wye River and the collision which diverted both channels of ice southward to form the Lydbrook Valley: www.geograph.org.uk/photo/1427688

www.geograph.org.uk/photo/133146

www.geograph.org.uk/photo/454739

Here is the valley through Lydbrook a bit further away from the Wye River, which is where the ice collision took place:

www.geograph.org.uk/photo/133140

www.geograph.org.uk/photo/1045033

This photo is taken from across the Wye Valley from Lydbrook. You can see the Wye Valley in front of you and the Lydbrook Valley, with the houses in it, between the two hills in the distance. This makes it easier to imagine how the two channels of ice collided while forming the Wye Valley and, diverting each other southward, formed the Lydbrook Valley: www.geograph.org.uk/photo/355420

This valley continues southward to Parkend: www.geograph.org.uk/photo/1319028 and Lydney.

BICKNOR

The collision between channels of glacial ice in what is now the Wye Valley, and which diverted each other's force southward to cut the Lydbrook Valley, was not quite so neat and simple. The proportion of ice coming through each end varied. For a time, the ice of the combined channel actually went in a different direction, and not through the Lydbrook Valley.

In the photo above, the ice also formed a much smaller and incomplete valley to the right (west) of the Lydbrook Valley. This is what we could call the Bicknor Valley because it is near the village of that name.

By the way, there is two villages named Bicknor. One is Welsh Bicknor, and the other is English Bicknor. Here, I am referring to English Bicknor. Welsh Bicknor is across the Wye River from Lydbrook. Both of these villages are actually in England. The reason that they are so-named is that a lot of Welsh Labourers (laborers) lived in one of the villages, so it became known as Welsh Bicknor.

Here are some photos of the valley at Bicknor. It forms a V with the origin of the Lydbrook Valley, pointing at their common origin. A small brook now flows through this valley. The Bicknor Valley was never completed down to the Severn Vale and it shows what the Lydbrook Valley must have looked like at an earlier stage of it's development:

www.geograph.org.uk/photo/454777

www.geograph.org.uk/photo/575830

www.geograph.org.uk/photo/454785

www.geograph.org.uk/photo/1543848

www.geograph.org.uk/photo/454791

www.geograph.org.uk/photo/73772

www.geograph.org.uk/photo/890991

By the way, look at how rounded are the Welsh Mountains in the distance. That means that the mountains are very old. One of my theories is that these mountains were once high enough to block the weather and that is why there is so much coal in Wales today. You can see "Coal Made Really Simple" on my geology blog.

THE WYE VALLEY

Let's go back to the scene at Symonds Yat: www.geograph.org.uk/photo/784049 and consider the Wye Valley from this point southward, until it joins the Severn River.

There are two places in this stretch of the Wye Valley where a branch river formerly joined the main river until changes in water flow after the end of the ice age caused the upstream section of the main river to either run dry or to become a very minor flow and the former branch to become the main river.

The first such instance is at Garnew, west of Symonds Yat. The former upstream of the river is completely dry and what was once merely a branch flowing into the main river has become that river.

The second is at Monmouth. The Monnow River was once the main river. It was a glacial route from just north of the Black Mountains.

At Redbrook, we have an example of a dead end glacial channel off the main Wye Valley. The ice cutting this channel turned around and headed back northward.

The ice covering the area around Coleford was maybe one or two kilometres thick and when it melted, it released a temendous amount of water. This meltwater carved drainage channels in the rock as it made it's way to the Wye Valley, which we can see today.

Two obvious drainage channels are at St. Briavels and Bigsweir. Two drainage channels nearly opposite each other at Brockweir and Tintern created an opposing flow, forming the loop in the Wye River that is there today.

The Coleford area was a basin of water collection. A large drainage river flowed from here to Newland. The basin at Coleford also drained into the Lydbrook Valley through what is now the valley around Speech House Road. From the woods to the north of Staunton, I see that two gorges have formed as channels by which meltwater flowed into the Wye Valley.

Look at the basin that Coleford is built in and the slopes of the basin within the town: www.geograph.org.uk/photo/765926

www.geograph.org.uk/photo/765947

www.geograph.org.uk/photo/766954

www.geograph.org.uk/photo/842699

Here are scenes of the Wye Valley, and valleys that once drained water and ice into it, at various points from Symonds Yat southward to union with the Severn River. The first two photos are of former drainage valleys which emptied into the Wye Valley and, the rest are of the Wye Valley itself:

www.geograph.org.uk/photo/908491

www.geograph.org.uk/photo/520170

www.geograph.org.uk/photo/707629
www.geograph.org.uk/photo/474580
www.geograph.org.uk/photo/1786549
www.geograph.org.uk/photo/11219
www.geograph.org.uk/photo/1499407
www.geograph.org.uk/photo/1402615

ROSS-ON-WYE

Moving northward, there is another valley which served as a mighty river at the end of the ice ages to drain meltwater, but which is dry today. The valley through the town of Ross-on-Wye has similarities to the one through Lydbrook. It was formed when glacial ice found a weak spot in the rock from a previous flow of water over that rock. The glacier was probably also diverted by ice piled against Leys Hill and Chase Hill. If there were a source of water where the Severn Vale is now located, this would be a major river flowing through Mitcheldean and Longhope.

On a map or the satellite imagery, it is easy to see that there is a major bend in the Wye River at Ross-on-Wye. This is because we have a situation similar to that at Monmouth and Garnew. This valley through the town was actually the main river following the ice age and the flow from Hereford was only a branch joining it. But as the volume of water from melting glaciers reduced, this became a dry valley, as it is today.

The glacial thrust which formed the valley at Ross-on-Wye came north of Chase Hill and was then deflected southward toward Drybrook and Mitcheldean by May Hill, the route is now followed by Rudhall Brook. There is a nearby valley extending south from the village of Coughton from glacial thrusts between Howle Hill and Chase Hill and this glacial route in successive ice ages seems to join the one that went through Ross-on-Wye on it's way to Drybrook.

Remember the view from the top of Coppet Hill, looking eastward. You see a closer hill and a further hill. The valley at Coughton is between the two and the valley at Ross-on-Wye is on the other side of the further hill. The buildings of Ross-on-Wye are visible: www.geograph.org.uk/photo/1187565

Here is a view of Chase Hill from Bridstow, across the Wye River from Ross-on-Wye: www.geograph.org.uk/photo/996598

In this photo, the two hills which affected the flow of ice which formed the valley through Ross-on-Wye can be seen from Bridstow. Chase Hill is the closer one and May Hill, with the famous clump of trees on the top representing the highest elevation in the Forest of Dean, is the further hill: www.geograph.org.uk/photo/996593

Here are views in the valley at Coughton: www.geograph.org.uk/photo/1128524 www.geograph.org.uk/photo/478727

The photo web site does not have any useful views of the valley in the town of Ross-on-Wye, but if you would like to have a look at it, you can go to my photo blog of Europe. Just go down to the "Town of Ross-on-Wye" and you will see the slope of this glacial valley. http://www.markmeekphotos.blogspot.com/

So, the glacial valley through Ross-on-Wye starts as one valley before it splits. The valley through Lydbrook started as two valleys, but ended up as one. The Wye Valley, from Symonds Yat southward, is one throughout.

DRYBROOK

The glacial movement from Ross-on-Wye continues to Drybrook. The resulting Drybrook Valley is parallel to that of Lydbrook, it continues southward past Cinderford, through Soudley and ultimately, Blakeney into the Severn Vale. On the other side of Plump Hill from the Drybrook Valley are parallel drainage valleys through Mitcheldean and Longhope.

On my photo blog of Europe, http://www.markmeekphotos.blogspot.com/, the third photo from the top is taken in the direction in which the glaciers would have came to carve the Drybrook Valley. The photo is taken looking northwest and is the same photo on the cover of my book "The Theory Of Primes". Notice the U-shape to the ground that is characteristic of glacial movement.

Here are views of the Drybrook Valley:

www.geograph.org.uk/photo/1355250

www.geograph.org.uk/photo/119212

While driving through the area on the main road, the A4136, the valleys through Lydbrook and Drybrook can be seen as dips in the road level. Here is the one representing the Drybrook Valley at the Nailbridge traffic light: www.geograph.org.uk/photo/1124521

A similar dip can also be seen in the A4136 as one passes Lydbrook. I would like to point out that there is another dip in the A4136 at Brierley, between Lydbrook and Drybrook. This is yet another glacial valley similar to the other two, except that it is far less developed at this point. If there are further ice ages, there will be a valley at Brierley similar to Lydbrook or Drybrook. Here is the dip in the road at Brierley: www.geograph.org.uk/photo/555202

GLACIAL IMPACT CRATERS

Now, still at Drybrook, let's go on to another phenomenon. A glacial impact crater is a land form which I discovered and documented several in the area of Niagara Falls. They are described in detail on my Niagara blog.

Basically, a glacial impact crater is formed when glacial ice is pressed up against a hill or escarpment during an ice age. When the ice age ends, the ice begins to melt. The glacial ice might be one or two kilometers thick so that it will be warmer at the bottom than at the top. As the ice melts faster near the bottom, the glacier becomes top heavy and may also fracture laterally.

The result is a vast slab of ice weighing millions of tons falling from a height of a kilometer or more and leaving a very distinctive crater in the ground.

Not only is Drybrook a valley, it is also a glacial impact crater. During the last ice age, ice moving along the main glacial route through the Severn Vale pressed up against Plump Hill in Mitcheldean. When the ice age ended, such a vast slab of ice crashed into the ground near the Drybrook Valley.

The result is what we now call Harrow Hill. The hill slopes downward in the direction in which the slab was moving in the same way as all of the other glacial impact craters.

Here is a view from the top of Plump Hill, looking out over the Severn Vale: www.geograph.org.uk/photo/268007 Notice the drainage valley at Mitcheldean in the foreground, which I mentioned earlier.

Here are views of Plump Hill from below: www.geograph.org.uk/photo/739896

www.geograph.org.uk/photo/739886

www.geograph.org.uk/photo/535732

Look at the slope of Harrow Hill at Drybrook: www.geograph.org.uk/photo/1355254

www.geograph.org.uk/photo/587502

On my photo blog, I took two photos of Harrow Hill from across the Drybrook Valley at Ruardean Hill which clearly show the flat slope of the hill characteristic of glacial impact craters, they are the eighth and ninth photos from the top http://www.markmeekphotos.blogspot.com/

As such slabs of ice melt, they tend to leave culverts through which the water flowed away as the slab melted. Bridge Road on Harrow Hill is built in the low-lying culvert through which the meltwater drained away into the Drybrook Valley: www.geograph.org.uk/photo/1355263

CINDERFORD

Now that we are familiar with glacial impact craters, let's move on from Drybrook to Cinderford. The same process happened here. Ice from the main glacial route through the Severn Vale pressed up against Littledean Hill. At the end of the ice age, a vast slab of ice crashed to the ground on what is today the landscape of Cinderford. It is flattened and sloping, just as is Harrow Hill.

Here is the view from the top of Cinderford, looking east over the Severn Vale. The centre (center) of London is about 150 km in this direction. The high ground on the other side is the Cotswold Escarpment: www.geograph.org.uk/photo/1459070

Now if we go a short distance and look in the opposite direction, we find ourselves looking at the slope formed by the vast ice slab which crashed down: www.geograph.org.uk/photo/1459193

www.geograph.org.uk/photo/728707

www.geograph.org.uk/photo/1456369

www.geograph.org.uk/photo/728595

Here are other views of the slope of Cinderford created by the glacial impact crater, notice the similarity to Harrow Hill: www.geograph.org.uk/photo/1039189

www.geograph.org.uk/photo/728568

Cinderford actually has two slopes, another one sloping down off the one caused by the impact crater. The lower, secondary slope is actually the side of the Drybrook Valley through which torrents of water flowed at the end of the last ice age. You can see in this view that the Cinderford area actually forms a bowl with Ruardean Hill in the distance. The lower part of this bowl was filled with water from the melting ice, which flowed out through Soudley and down to Blakeney. See the bowl: www.geograph.org.uk/photo/854797

Here is another view that conveys a sense of the bowl from the bottom: www.geograph.org.uk/photo/759954

These scenes are of the secondary slope in Cinderford, sloping down from the main slope, created by the impact crater, to the slope created by the flow of meltwater out through Soudley:

www.geograph.org.uk/photo/728705

www.geograph.org.uk/photo/728712

www.geograph.org.uk/photo/132478

www.geograph.org.uk/photo/728719

In this photo, at the centre of Cinderford, you can see the secondary slope angling downward off the main slope: www.geograph.org.uk/photo/132426

This is a photo taken closer to Soudley, where the water that went past Cinderford flowed out on it's way to the Severn Vale: www.geograph.org.uk/photo/1605897

This flow ended up at Blakeney, closer to the Severn River. Here is a view of the valley there: www.geograph.org.uk/photo/533100

The main flat slope of Cinderford, shaped by the impact crater can be seen in the fifth and sixth photos from the top on my photo blog, http://www.markmeekphotos.blogspot.com/ Cinderford is the town in the distance in these views taken from Drybrook. If you look closely, you can even see the gap in the distant hills over to the right where the water ultimately flowed out at Soudley.

U-SHAPE

I would just like to show a couple of more scenes of that U-shape that moving glaciers tend to leave on the ground. This U-shape to the ground is to be seen all over the Forest of Dean, looking northwest from Yat Rock, looking northwest from Drybrook and at the bottom of Lydbrook. Here are more such scenes which I noticed:

www.geograph.org.uk/photo/1815171

www.geograph.org.uk/photo/683497