292 ON SOME LACUSTRINE DEPOSITS, ETC. 



becoming dammed, formed a miniature lake, into which was 

 washed the fine white mud usually carried by streams flowing 

 from glaciers. This being deposited in the still and probably 

 deep water of the small lake formed the deposit of white clay 

 which we now find so well preserved in the south cutting. 

 There is no doubt that the undulation in the white clay which 

 was traced right across the cutting in a north-easterly direction 

 was caused by a current or eddy in the stream of water 

 coming into the lake, probably as it flowed swiftly round the 

 eastern end of the outlier of Magnesian Limestone. The 

 general shape, gradual thinning out, and intermingling with 

 the other coarse deposits of the white clay, all go to prove its 

 lacustrine origin. The stream having now cut its way back 

 so as to erode the yellow sands, which must have lain across 

 its path, quickly removed them, and deposited them over 

 the white mud which was gradually silting up the lake. 

 The deposits seen in the north cutting and on the north side 

 of the south cutting are part of those formed near the very 

 edge of the lake, and are therefore found much intermingled 

 with drift and coarser fragments. Owing to some change in 

 the climate, the ice line again crept down to lower levels; and 

 glacial conditions again intervening, a deposit of drift was left 

 over the whole of the lacustrine deposits. 



Of necessity these deposits would be very irregular, 

 especially near the edges of the water, yet their general 

 character and position confirm the above explanation. 



The author would acknowledge his indebtedness to Mr. T. 

 Charles Cook, of the Dean and Chapter Colliery, for the 

 numerical data of the sections, and for his kind preparation 

 of the sketch map of the district. 



