Ah -- what a peaceful scene! The Goring Gap, conventionally portrayed as being well to the south of the "Pleistocene ice limit" of southern England, but also conventionally described as having been cut initially by glacial meltwater spilling southwards from an ice-dammed lakes on the northern flank of the Chiltern Hills and the North Wessex Downs. Some say the ice edge was far away, and others say it was close by, since there is not much evidence for an extensive "Lake Oxford" in the literature.
Anyway, I was intrigued by this dilemma and came across an interesting MA thesis written by Cherry Antoinette Goatman in 1961. It's a good thesis, in which she examines carefully the assorted arguments for the formation of the Goring Gap and the wind gaps or channels on the crest of the Chilterns. I append some extracts from her thesis, but suffice to say that having read it and pondered on the evidence she brings forward, it seems pretty obvious that the Chilterns have been glaciated, and that meltwater (subglacial? that's more difficult to sort out....) was responsible for the spectacular valleys of which the Goring Gap is the best known.
SOME ASPECTS OF THE GEOMORPHOLOGY OF THREE CHILTERN WIND-GAPS
by CHERRY ANTOINETTE GOATMAN
UNIVERSITY OF LONDON M. A. GEOGRAPHY I96I
Although there have been many publications dealing with the general geomorphology of the Central Chilterns and Vale of Aylesbury, none has yet dealt satisfactorily with the problems of the age, origin and development of the wind-gaps and their associated superficial deposits. Three gaps, the Wendover, Tring and Dagnall, have been selected for detailed study. The morphological features have been mapped on the 6 inch scale, the soils and gravels examined, and the pattern of soil series dis tribution related to the landforms. The various features of the gaps have then been compared, and suggestions made as to the possible evolution of the gaps.
The principal hypotheses so far put forward postulate that the gaps were initiated: 1) by pre-glacial rivers; 2) as glacial overflow channels ; 3) by marine erosion in Pliocene times; 4) by pre-glacial rivers and modified by glacial melt-water. The last of these, with amplifications, seems most in accord with the field evidence accumulated in the course of the present study. Thus a hypothesis of major south-east flowing captured Mid- Tertiary consequents is submitted for the origin of the wind-gaps at Wendover and Tring. Subsequently each gap was affected by the Calabrian marine invasion and later modified both by glacial and periglacial processes.
Deposits
.............. more recent deposits on the dip-slope present a complex variety and have been variously interpreted (Fig, 4 ). Sand and shingle of early Pleistocene age (Calabrian) has been located by Wooldridge (1927) at an elevation of some 600-650 feet. Brickearth (Hull and Whitaker I86I), Pebble Gravel (Jukes-Browne and White I908), Clay-with-Flints (as delimited by the Geological Survey) and Pebbly Clay and Sand (Sherlock 1947) have all been grouped together by Loveday (1958) under the general heading of Plateau Drift, which has a total thickness or some 30-40 feet. This drift is evidently a product or one or more or the early Pleistocene glaciations when the Chilterns possibly supported a local ice cap, according to Wooldridge (1938),and were certainly subject to the effects of periglacial climates. Loveday's terrace deposits (the Plateau Gravel of Jukes-Browne and White, I908, and the Glacial Gravel of the Geological Survey) generally lie below 500 feet and are younger than the Plateau Drift.
They have recently been thoroughly worked over in connection with the evolution of the Thames. Patches of Glacial Gravel are also mapped by the Geological Survey on the northern margins of the Vale of Aylesbury. The Valley Gravels and Gravels opposite Chalk Gaps are thought to be head deposits resulting from solifluction during more recent Pleistocene glaciations and are intermingled with more recent hill-wash and alluvium.
The wind gaps and channels
p 32 There are erratics at 462 feet on Southend Hill (Grid Ref. 920 165) in the Vale of Aylesbury......
Sherlock citations: "It is highly probable that the Chiltern Hills held up an ice-sheet..... It is likely that, on the retreat of the ice, channels would be cut in the chalk scarp by the water produced by the melting ice and snow". In 1935, he referred to these features again (Page 53) as "cut out of the chalk by the melt-waters from the plateau".
Hawkins, in 1923, went even further along these lines. He suggested that the outlines of the both Goring Gap had been shaped by a tongue of ice and melt-water from a glacial lake but produced no very convincing evidence for this. He also mapped three stages in the retreat of this assumed ice mass (Fig. 9 ). He felt there were sufficient grounds for mapping the ice, at its farthest extent, as penetrating to the watershed of the Wendover Gap and to Berkhamsted in the Tring Gap. The second stage was thought
almost to have reached the Wendover watershed and as far as Horthchurch in the Tring Gap. The third and final stage was limited to areas below the 300 foot contour.
THE GLACIAL MELT-WATER THEORY
This hypothesis attracted many of the earlier workers in the area and, in spite of the fact that some of the later workers felt they had conclusively disproved it, similar ideas still reappear in different guises in some of the general literature. The theory in essence requires the entrance of a tongue of ice into the Vale of Aylesbury from the north-east, the impounding of a lake between the receding ice front and the Chiltern escarpment, and the overflow of its waters through spillways breaching the Chalk cuesta.
.............. more recent deposits on the dip-slope present a complex variety and have been variously interpreted (Fig, 4 ). Sand and shingle of early Pleistocene age (Calabrian) has been located by Wooldridge (1927) at an elevation of some 600-650 feet. Brickearth (Hull and Whitaker I86I), Pebble Gravel (Jukes-Browne and White I908), Clay-with-Flints (as delimited by the Geological Survey) and Pebbly Clay and Sand (Sherlock 1947) have all been grouped together by Loveday (1958) under the general heading of Plateau Drift, which has a total thickness or some 30-40 feet. This drift is evidently a product or one or more or the early Pleistocene glaciations when the Chilterns possibly supported a local ice cap, according to Wooldridge (1938),and were certainly subject to the effects of periglacial climates. Loveday's terrace deposits (the Plateau Gravel of Jukes-Browne and White, I908, and the Glacial Gravel of the Geological Survey) generally lie below 500 feet and are younger than the Plateau Drift.
They have recently been thoroughly worked over in connection with the evolution of the Thames. Patches of Glacial Gravel are also mapped by the Geological Survey on the northern margins of the Vale of Aylesbury. The Valley Gravels and Gravels opposite Chalk Gaps are thought to be head deposits resulting from solifluction during more recent Pleistocene glaciations and are intermingled with more recent hill-wash and alluvium.
The wind gaps and channels
p 32 There are erratics at 462 feet on Southend Hill (Grid Ref. 920 165) in the Vale of Aylesbury......
Sherlock citations: "It is highly probable that the Chiltern Hills held up an ice-sheet..... It is likely that, on the retreat of the ice, channels would be cut in the chalk scarp by the water produced by the melting ice and snow". In 1935, he referred to these features again (Page 53) as "cut out of the chalk by the melt-waters from the plateau".
Hawkins, in 1923, went even further along these lines. He suggested that the outlines of the both Goring Gap had been shaped by a tongue of ice and melt-water from a glacial lake but produced no very convincing evidence for this. He also mapped three stages in the retreat of this assumed ice mass (Fig. 9 ). He felt there were sufficient grounds for mapping the ice, at its farthest extent, as penetrating to the watershed of the Wendover Gap and to Berkhamsted in the Tring Gap. The second stage was thought
almost to have reached the Wendover watershed and as far as Horthchurch in the Tring Gap. The third and final stage was limited to areas below the 300 foot contour.
THE GLACIAL MELT-WATER THEORY
This hypothesis attracted many of the earlier workers in the area and, in spite of the fact that some of the later workers felt they had conclusively disproved it, similar ideas still reappear in different guises in some of the general literature. The theory in essence requires the entrance of a tongue of ice into the Vale of Aylesbury from the north-east, the impounding of a lake between the receding ice front and the Chiltern escarpment, and the overflow of its waters through spillways breaching the Chalk cuesta.
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Like all theses, this one is a product of its time -- with mentions (which one would never get nowadays) of cycles of erosion and marine erosion at the time of a "Calabrian Sea". But all that was very popular in London University in 1961, so she had to go with the flow...... However, at Rothamsted and at the Little Heath SSSI there are traces of Red Crag shoreline deposits, probably dating to Late Pliocene / Early Pleistocene times, prior to local crustal uplift.
Interestingly enough, in the 1970s assorted researchers referred to "the Chiltern Drift" and suggested it was older than the Anglian -- but they were never very specific as to where this "drift" was located, and what its characteristics were, apart from mentioning that it contained northern erratics.
6 comments:
Is anyone able to enlighten us about how, another GAP, the so - called Lavington Gap was formed? I noticed this term was used (without any explanation) in the renowned field archaeologist Leslie Grinsell's "The Archaeology of Wessex" (1958). It enables a route up onto Salisbury Plain from the north, towards Tilshead (which has 6 Neolithic long narrows within its parish), and onwards to Shrewton, all along the A360, which starts in Devizes. Stonehenge and its modern Visitor Centre is just off the A360 south - east of Shrewton. The ancient Wessex Ridgeway runs across the Gap.
Don;'t know that one -- there are a lot of gaps around, and some pretty spectacular river valleys in the vicinity of Bath and elsewhere. many of the valley6s are classic misfits, and must relate to times of high-volume flow. That's why, over the years, there has been much speculation about impounded lakes and overflows -- Lake Harrison, Lake Maw, Lake Oxford amd so forth.
From a prehistoric settlement and movement point of view, has enough thought been paid to how the Lavington Gap enabled some of the movement and links of Mesolithic & Neolithic peoples living in those two ultra - significant areas of Greater Avebury and Stonehenge and surroundings? Just look at a map of the physical geography for Avebury towards Tilshead/ Shrewton/ Stonehenge, and imagine that map overlaid with long barrows etc.
We may already have the Stonehenge and Avebury World Heritage Site, but do we think enough about the routes and interactions between them?..........
Avebury and Stonehenge are the two separated components of the existing World Heritage Site. They are, however, two separated enclaves within the very rich archaeological landscape of Wiltshire/Wessex: a nonsensical way to study the wider area/region.
Strikes me the archaeological writing and researching fraternity have, by zooming in on each of these two
"enclaves" , Avebury and Stonehenge, neglected the intervening landscapes a great deal. As stated previously, the Lavington Gap may have been a vital proponent in creating a significant route of interconnection. Devizes stands between these two enclaves.
Well, this is of course what Barclay and Brophy have been saying -- the aggrandisement of Stonehenge/Durrington/Avebury at the expense of all else. It's all to do with marketing and money......
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