18 



a. Warp (of Mr Trimmer) forming pockets or channels. 



h. White sandy brick-earth (much contorted). 



c. Yellowish sandy earth. 



d. Fine sandy gravel. 



e. Yellowish brick-earth. 



f. Fine gravel, more contorted than the contiguous layers. 



g. Sand, 



The sands contain Bithinia, &c. 



The irregularities observable between a and h, which Mr Fisher 

 describes as similar to the tenons in the framework of a dis- 

 sected puzzle, are considered to be the sections of channels of 

 drainage. In the Cambridge gravel pits, he says, "the percola- 

 tion and consequent erosion seem to have taken place in the 

 layer beneath the ductile Clay, which is folded into such 

 remarkable forms." 



He remarks with truth that these contortions must in some 

 way or other have resulted from sub-aerial causes and cannot 

 be due to any kind of ice-action. 



1866. In "A Sketch of the Gravels and Drift of Fenla.nd\" 

 Mr Seeley describes the Drifts in this part of Cambridgeshire. 

 Following Prof. Sedgwick's triple Classification and commencing 

 with the Boulder Clay, he notices its colour, thickness, contents 

 and extent over the high ground immediately West and N.W. 

 of Cambridge. He gives a section of the Fossiliferous Gravel 

 at March, from which this marine deposit would appear to be 

 intercalated between two sheets of Boulder Clay. "Tracing 

 this Gravel south to Wimblingdon, near the railway station, the 

 deposit, quite at the surface and only a foot or two thick, rests 

 on one of the thin stonebands so common between the Oxford 

 and Kimmeridge Clays. It is a fine sandy gravel with the 

 usual shells; but the argillaceous limestone rock was drilled 

 with the burrows of Pholades, the shells being still in the holes." 



He proceeds to say that the gravels are somewhat con- 

 tinuously spread southwards by Chatteris, Somersham, Earith, 

 St Ives and Willingham to Swavesey, and that he had found 

 marine shells in gravel taken from old pits near Drayton Gate 

 House. From the gravel at March he cites 20 species of 

 MoUusca. 



1 Quart. Jourii. O'eol. Scr. Vol. xxii. p. 470. 



