15 



for by the fact that the Cambridge Boulder Clay and the 

 Cromer Till were at this time thought to be one and the same 

 deposit. 



1847. An Essay on the "Farming of Cambridgeshire" is to 

 be found in the Journ. Roy. Agric. Soc. Vol. vii. p. 35, by 

 S. Jonas Esq. A brief outline of the Geology of the county is 

 here given, and illustrated by two rough diagrammatic sections, 

 one from Gamlingay to Madingley, the other from St Ives to 

 Swaffham. He remarks that the southern and central portion 

 of the county is light land, consisting of chalk covered in places 

 with diluvial sands and gravels ; but that the eastern part 

 adjoining Suffolk and Essex has a heavy clay-soil which requires 

 draining. The western side of the county is also much covered 

 by a tough tenacious clay- soil, though the lower lands afford a 

 good deep staple. Lastly he mentions the Isle of Ely and the 

 Fen lands in the northern part of the county. 



1861. In a supplement to a lecture "On the Strata near 

 Cambridge and the Fens of the Bedford Level," published in 

 18G1, Prof. Sedgwick gives a much fuller account of the Drift 

 deposits. The evidence for a recent glacial period had then 

 been more fully developed, and the Professor assumes the sub- 

 mergence of the British Isles and the transport of Drift by 

 means of ice-floes and icebergs. For the resulting accumulations 

 he adopts the name of Diluvial Drift, but still groups with them 

 the higher and older portions of the Cam Gravels. The term 

 Boulder Clay is now used instead of Brown Clay, by which 

 name he had formerly designated it, and he notices that "In all 

 places, where it is seen near Cambridge, it contains many rolled 

 fragments of Chalk ; and the abraded Chalk is sometimes so 

 abundant as to give to the Clay a tinge of light grey," he briefly 

 indicates the distribution of this Boulder Clay over the Eastern 

 Counties, referring to Mr Barrett's map (published in 1859) for 

 its disposition near Cambridge. 



He next describes the coarse Gravels found on the Harston, 

 Stapleford, and Gog-Magog Hills, — he observes that specimens 

 of many of the great rock formations of England may be 

 obtained from these deposits, and instances some found by him- 

 self.... "None of the rock specimens," he says, "are perfectly 

 angular. Tliey have been partially rounded, and a few of 



