Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/152

114 114 S. V. WOOD, JTTN., AND F. AY. HARMER ON THE Boulder-clay, or Upper Glacial, which covers so much of England and Scotland, and of which only the oldest or first-accumulated por- tion is present in East Anglia, seems to us to have arisen from the state of things we now propose to describe. As the submergence proceeded, and the sea, after occupying, as fiords, the interglacial valleys of East Anglia, gradually rose over the tablelands, so did the land-ice on the mountain districts of the north of England accumulate and descend over the lower ground until it formed a continuous sheet, which ultimately enveloped probably every thing as far as it extended. The thickness of that portion which descended over Yorkshire may eventually have amounted on the lowest ground to 1200 or 1500 feet, though very likely it was much less ; but though enveloping high and low ground alike, its principal motion, and with it that of its moraine profonde, was, as it seems to us, through the greater valleys only, to their seaward termination. Thus a part moved through the great valley of the Tees, another part through the great valley of Pickering, while a third moved through the smaller valley of the Humber. None of these three, however, concern us in relation to the East- Anglian deposits further than that we recognize in that portion of the moraine which passed through the valley of the Humber and forms the lower part of the Glacial clay of Southern Holderness, or that in which chalk debris is abundant, a deposit coeval with the Upper Glacial of East Anglia. The moraines of the first two branches, which were contemporaneous with this, were, it seems to us, extruded beyond the present coast- line, and some way out in the present North Sea. The largest branch of the Yorkshire portion of the sheet is that with which we have to concern ourselves, as it is that to which the Upper Glacial clay of East Anglia owes its origin. This branch moved southwards over Lincolnshire, as is proved, not only by the profusion in that clay of Jurassic debris derived from the troughs which lie between the chalk escarpment and the respective Oolitic and Liassic escarpments of that county, but also by the occurrence in it of lumps of the red chalk * which underlies the white chalk of that county and of Yorkshire, but which ceases near Hunstanton, in the extreme north-west of Norfolk. This red chalk debris has travelled in one direction as far as the brow of the Thames valley, where it occurs in association with the hard stony chalk of York- shire and Lincolnshire, which constitutes the principal proportion of the debris in the Upper Glacial clay of that district as well as of East xlnglia in general ; and in similar association it has found its way as far as the Cotteswolds, where it occurs in gravels which pro- bably represent both the Middle and the Upper Glacial of East Anglia, that clay dying out about thirty miles north-east of the Cotteswolds. These gravels have been traced by Mr. Lucy t to alti- certain horizons of the Chalk in Lincolnshire and Yorkshire, but are confined to those counties. t "The gravels of the Severn, Avon, and Evenlode, and their extension over the Cotteswold Hills," Cotteswold Club, April 1869.
 * Some of these lumps may be fragments of the pink bands which occur at