Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/255



The rubble rests on the summit of a conical hillock, the sides of which consist of naked grey chalk; than which one can hardly suppose a situation more unfavourable for the accumulation of alluvial matter; at any rate why is not this found in as great abundance on the Hanks as on the summit of the hillock? This looks like the partial destruction of an alluvial level by some subsequent cause, the discovery of which I leave to more learned members of the Society.”

Thus far Mr. Warburton. With respect to the hard chalk pebbles it may be proper to remark, that in some parts of the chalk formation a harder bed is found, of a close grain and compact texture, which might very well supply the material from which these pebbles have been formed. This bed may be seen at Sudbury in Suffolk, and I have also observed it in some parts of the Yorkshire wolds. The striped variety of flint is also to be met with in the ordinary chalk of the same hills. I have before observed that a distinction must be made betwixt this deposit and the ordinary gravel found at a lower level; and in fact throughout the Isle of Ely such a distinction is universally admitted, the one being called the white gravel and the other the red. The same distinction is known in Dorsetshire, as I learn from De Luc's Travels, vol. ii. p. 77, in a passage particularly illustrative of these two deposits.

It would be unnecessary to trouble the Society with any observations on the chalk bed with flints, as I am not aware that they present any thing new, and their phenomena may be studied in other parts of the island to greater advantage. I pass therefore to the lower beds or grey chalk, which composes by far the greatest part of the hills of Cambridgeshire. These beds, as is well known, contain no flints, but, not uncommonly, dispersed masses of the