Geology of Cambridgeshire, '247 



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 flanks as on the summit of the hillock ? This 

 looks like the partial destruction of an alluvial level by some sub- 

 sequent cause, the discovery of which I leave to more learned 

 members of the Society." 



Thus far Mr. Warburton. With respect to the hard chalk peb- 

 bles 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 York- 

 shire 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 obser- 

 vations 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 



