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III.—American “Surface Geology,” and its Relation to British. With some Remarks on the Glacial Conditions in Britain, especially in Reference to the “Great Ice Age” of Mr. James Geikie

Published online by Cambridge University Press:  01 May 2009

Searles V. Wood Jun
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Extract

Numerous buried channels filled with drift occur over Ohio and the neighbouring states forming the St. Lawrence basin. Some of these penetrate the water-parting, and formed, according to Prof. Newberry, waste weirs through which the lake waters of the St. Lawrence basin escaped into the valley of the Mississippi, as the land rose and the sea retired from that valley.

Type
Original Articles
Information
Geological Magazine , Volume 4 , Issue 12 , December 1877 , pp. 536 - 551
Copyright
Copyright © Cambridge University Press 1877

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References

page 539 note 1 See S. V. Wood, Jun., and Harmer, F. W., in Q.J.G.S., 02. 1877, p. 74Google Scholar, and Harmer, F. W. in same, p. 134Google Scholar.

page 541 note 1 A considerable spread of coarse rolled flint gravel in West Norfolk resembling cannon shot seems to have resulted from similar current action during the formation of the Upper Glacial chalky clay, upon which in some instances it seems to rest.

page 541 note 2 The position of the beds thus referred to is shown in the Geological representation of Ordnance Sheets 1 and 2, which I made, and in the year 1866 placed in the Library of the Geological Society, with a manuscript memoir and sections in illustration of it. It is also shown in the map at p. 348 of Vol. III. Geol. Mag. 1866.

page 542 note 1 Darbyshire, , Geol. Mae. 1865, Vol. II. p. 293.CrossRefGoogle Scholar

page 542 note 2 The Upper Glacial of Middlesex and Essex contains little other chalk than the hard form of that material characteristic of Yorkshire and Lincolnshire; but in Norfolk a good deal of soft chalk is intermingled, and in the case of the morainic clay in the valleys of that county produced, as mentioned further on, by glaciers protruding tongue-like from the great mass of inland-ice, the chalk debris seems mostly of the soft character of the valley floor on which it rests. The fact that the chalk so abundant in the Glacial clay of Middlesex and Essex is all of the hard kind (at least if any of the soft is present it is so occasional that it has escaped my notice), seems to me to go a long way in proof of this clay not being what Mr. Geikie makes it out to be,—the submoraine in situ of a glacier which reached to the Thames Valley; for if so the chalk debris would be that derived from the counties of Essex, Middlesex, Herts, Cambridge, Suffolk, and Norfolk exclusively, instead of, as it appears to be, chalk derived in chief part, if not exclusively, from Lincolnshire.

page 543 note 1 This trough is that lying between the north scarp of the Chalk Wold and the slope of the Eastern Moorlands formed mostly of rocky Jurassic beds. Its eastern end is now blocked up by the last of the morainic clay which its glacier engendered, so that the drainage flows in the opposite direction to that in which the moraine travelled to the sea, viz. westwards and round the north-west angle of the Wold, and thence southwards to the Humber, west of the Wold scarp. During the Contorted Drift the Pickering glacier, I conceive, travelled perhaps 50 miles on both its sides over chalk; but at the period of the commencement of the purple clay it had shrunk back so that one side only touched the chalk, and this for a few miles only, and as the purple clay deposit proceeded, it gradually shrank from the chalk altogether.

page 546 note 1 I learn from M. E. Vandenbroek of Brussels that the Crag to a depth of 415 feet has been sunk through at Utrecht, in Holland, under 760 feet of (so-called) Quaternary accumulations, the boring at that depth (1175 feet) being still in sands whose fossils agree with the Coralline Crag, and not those of the earliest of the Belgian Crag-beds. This seems to me to show that the bed of the North Sea, undisturbed by the Scandinavian glacier-ice, has been tranquilly receiving sedimentary accumulations from the commencement of the Pliocene period up to the conversion of parts of it into land at the close of the Glacial period.

page 546 note 2 See Gavey in Quart. Journ. Geol. Soc. vol. ix. p. 295Google Scholar, for full description of the Mickleton cutting; also Hull, in vol. xi. p. 477.Google Scholar

page 546 note 3 “The Gravels of the Severn, Avon, and Evenlode, and their extension over the Cotteswold Hills,” by W. C. Lucy, read April 7th, 1869, before the Cotteswold Club, and printed separately.

page 547 note 1 Geol. Survey Memoir on the Isle of Wight.

page 547 note 2 Codrington, Quart. Journ. Geol. Soc. vol. xxvi. p. 528.Google Scholar

page 547 note 3 I have in various papers during twelve years past, and particularly in one on the Weald Valley denudation in Quart. Journ. Geol. Soc. for 1871, urged that the disturhances in which the rectilinear upcasts of the Isles of Wight and Purbeck, as well as those of the Hogsback and Portsdown Hills, originated, took place at this time; viz. the close of the Glacial period and beginning of what we in England have been accustomed to call the post-Glacial; and it is interesting to me to find that Mr. Prestwich, in a paper read in the year 1874 (Q. J. G. S. vol. xxxi. p. 29Google Scholar), makes out that during the Glacial period that portion of the Purbeck and Wight anticlinal which is continued north of Portland Isle was submerged, and then upheaved and subjected to excessive denudation, though he does not admit the general submergence of the South of England.

The section given in the Geological Survey Memoir of the Isle of Wight through Headon Hill, with that in the Memoir on the London Basin through Cæsar's Camp (vol. iv. p. 376), are, it seems to me, not reconcilable with anything less than this general submergence; and show to my mind clearly the excessive denudation which accompanied the acute upthrow of these rectilinear ridges, just as Mr. Prestwich shows it has done the portion of one of them which is continued through the Portland district.

The restoration map No. II. of the plate to the paper by myself on the Weald above quoted shows what I regard as the distribution of land and water at that particular stage of this emergence, when the oldest part of the gravel lying within the Thames Valley commenced to form and when the West and South of England were to a great extent still submerged.

I ought to add also that MrFisher, O. in 1868 (geol. mag. Vol. V. p. 99)Google Scholar, suggested that the lofty gravels over the Southern counties represented the Upper Glacial. At that time I regarded them as somewhat later, and as having accumulated after the glacial clay had been removed from that part of England by denudation, but I have for several years past given up this view in favour of that of Mr. Fisher.

page 549 note 1 Where this cutting was carried through, sand had rested on sand, viz. the Middle Glacial on the Bure Valley beds; but a pit about a quarter of a mile west, of old date, showed the Middle Glacial sand resting on the Contorted Drift, which in that neighbourhood is uncontorted. The valley plough referred to in the text had here contorted the two together, and so given rise to this exceptional feature.

page 550 note 1 The limit up to which this inland-ice pressed upon and destroyed all the preceding glacial deposits is marked, as nearly as can he defined, by a line which, starting in North-west Norfolk, a little east of Docking, runs south between Swaffham and East Dereham, and between Thetford and East Harling, where the ice began to draw in to form the glacier-tongue which passed through the Waveney Valley; from whence it runs by Bottesdale, south of which the glacier-tongue through the Gipping Valley went off. From thence the line runs westwards, and is more difficult of definition. The tongue which passed down the valley of the Wensum and Yare probably went off near the starting-point of this line.

page 550 note 2 I think it, however, probable that the chalky clay and underlying (Middle Glacial) gravel do not possess the regular horizontality which Mr. Prestwich gives to them; and also that between them and the chalk some of the Contorted Drift, out of which the valley was first interglacially excavated, may be present. The representation given by Mr. Belt in the Quart. Journ. of Science for 1876 does not in any respect agree with my view of the facts of the case.