LATER TERTIARY GEOLOGY OF EAST ANGLIA. 117 below the capping of Postglacial clay (called by us and by Mr. Rome the Hessle clay*), this debris disappears altogether. Following the cliff northwards we see precisely the same change taking place in a horizontal direction, until, as we near Elamborough Head, where the chalk floor rises above the beach, this debris disappears from the clay altogether, and the clay which capped the cliff further south, and was underlain by a great thickness of clay filled with rolled chalk, rests upon the Chalk direct, save where in the old buried gorges of the chalk floor it is underlain by moraines formed purely of rolled chalk that occupy these gorges, and are evidently connected with the great mass of clay which is so full of the same material further south. Thus the clay without chalk spreads for a certain distance southwards over the clay with chalk, but gradually takes its place northwards ; and this is the same kind of sequence and relation which obtains between the Upper and the Middle Glacial. Let us now suppose that the branch of the land-ice to which the Upper and Middle Glacial of East Anglia were due extended south- wards in such a way that, avoiding all but the extreme west of Norfolk, it touched the west of Suffolk a little east of Thetford (ploughing out and destroying in its course whatever beds of Lower Glacial age may have been there), and that from this point its edge trended south-westwards by Newmarket and along the chalk escarp- ment of Cambridgeshire to Baldock, whence, after making a little bend towards Biggleswade, it stretched to the borders of Buck- inghamshire. This boundary would (except so far as the excess of altitude above 300 feet causes the absence of the formation) roughly define the westerly limit of the Middle Glacial in Norfolk, Suffolk, and Essex, and its northerly limit in Hertfordshire and Bedfordshire. Our knowledge of the Midland Counties does not allow us to define the western continuation of this boundary with precision; but gravels and sands underlying the Upper Glacial (chalky portion) occur in Buckinghamshire, Warwickshire, and Leicester- shire, west of a line drawn northwards from the termination of the already defined boundary towards Leicester, though these are fre- quently (and, indeed, generally in a north-westerly direction) over- lapped by the Upper Glacial resting directly on the older formations. These gravels seem to represent the Middle Glacial, both in position and also in some degree in extent of outspread ; but the gravels inferior to the Upper Glacial which occur within the space described by this boundary are so extremely rare and sporadic that they seem due to some local action during the accumulation of the Upper Glacial, and not to belong to our East- Anglian formation f.
- The capping bed of Hessle clay does contain chalk debris, but not of the
rolled character of the Glacial clay below, being more or less subangular. t An extensive outspread of sand occurs in Lincolnshire on the Liassic and Oolitic escarpments ; but this can be traced eastwards as passing over the Upper Glacial. There is also a considerable sand formation in the north of Notting- hamshire; but, so far as we are able to judge, this seems connected with the later part of the Upper Glacial, viz. that of which we have spoken as taking the place of and partially overlying the clay containing chalk debris, or else with the Hessle sand. i 2
