EROSION" OF THE GLACIAL DETFT. 



97 



rence, and if these are 

 caught in troughs deposits 

 of sand quickly accumu- 

 late in the receptacles. 

 After heavy rains the 

 quantity of sand deposited 

 by even tiny springs is 

 very considerable. 



Where the drainage is 

 insufficient to maintain 

 permanent springs, a stra- 

 tum of a soft puddly nature 

 is produced by the con- 

 stant oozing-out of under- 

 ground water. There are 

 other outlets which are 

 active only during the con- 

 tinuance of very heavy 

 rain, acting as storm- 

 overflows for the ordinary 

 underground drainage. 



One and all, however, 

 issue from underground 

 charged with matter de- 

 rived from the subterra- 

 nean erosion of the clays, 

 sands, and gravels under 

 or through which they 

 have passed. Waste so 

 constant cannot have con- 

 tinued for a long period 

 of time without leaving 

 evidences of its effects. 



For instance, in Ithell's 

 sandpit (see fig. 1), the 

 sauds and gravels be- 

 neath the Upper Boulder 

 Clay have been proved for 

 30 feet without reaching 

 the rock (Bunter Pebble- 

 beds). If the clay, sand, 

 and gravel were of a uni- 

 form thickness across the 

 whole line of section from 

 S.S.E. toN.:^.W.,theclay 

 would be upon the horizon 

 A-A, and the sand and 

 gravel should crop out at 

 Z-Z instead of at B-B 

 It should be noticed that 

 the height of the clay 

 from ridge to ridge is uni- 

 form throughout, so that 

 an observer at either end 

 has an uninterrupted view 

 across. 



If A-A represents the 

 a. J. G. S. No. 189. 



rji -^ Ithell's sandpit. ?= 



!l|j||i 



ii 



m 



l'°o 

 lis." 



Streamlet No. 1. 



, Valley No. 1. 



.__! Streamlet No. 2. 



Chester and Birken- 

 head Bead. 



3 



0^* 



"? 



^ 



^ 



I 





