MR. WM. SHONE OlS^ THE SUBTERRAlTEAlSr 



9. The Subterranean" Erosion of the Glacial Drift, a probable 



CAUSE of SUBMERGED PeAT- and FoREST-BEDS. By Wm. ShONE, 



Esq., P.G.S. (Read December 9, 1891.) 



The Drift of the N.W., N.E., and Central England covers a large 

 area of the Triassic Series, composed of interst ratified hard and 

 soft rocks, giving rise to very unequal denudation of the various 

 members of the series. The Triassic area is consequently of an 

 undulating character, and the Drift which covers it like a mantle 

 partakes of the undulating nature of the rocks it overspreads. 

 The Drift upon the sides of the valleys has, at short intervals, been 

 cut into minor valleys by the rain coursing down their slopes. 

 The minor valleys cut out of the Drift should be carefully distin- 

 guished from the larger valleys covered with Di^ift^ for the latter 

 appear to follow the contour of the pre-Glacial land surface. 



Every minor valley has its small streamlet, which in dry weather 

 is most frequently a very insignificant watercourse ; during heavy 

 falls of rain, however, such tiny rivulets become swollen into large 

 and rapidly-flowing brooks, charged with densely turbid water 

 derived from the clays,, sands, and gravels of the Drift. 



The section (fig. 1) is across two such minor valleys. At 

 the S.S.E. end is situated the sandpit, with a face of the pit at 

 right angles to the line of section. Under the surface-soil the pit 

 has a covering of Upper Boulder Clay (varying from 2 to 6 feet in 

 thickness) resting upon Middle Sands and Gravels. About 6 feet 

 beneath the base of the Upper Boulder Clay there was a band of 

 clay a few inches thick in the underlying sands and gravels. After 

 a very heavy fall of rain in November 1890 I found the sands and 

 gravels between these two beds of clay to be full of large holes, 

 through which the subterranean water that had percolated between 

 the clay-beds had escaped. Where the sands and gravels had been 

 forced from under the Upper Clay, many tons of the latter had fallen 

 into the bottom of the pit. 



This occurrence led me to consider what would have become of 

 the sudden rush of subterranean water through the sands and gravels 

 lying under the Upper Boulder Clay had there been no artificial 

 outlet into the sandpit. If it had found an outlet along an inclined 

 plane it would have forced along the fine sands and gravels from 

 beneath the more impervious clay to the place of escape. The search 

 for the probable direction of the underground drainage resulted in 

 finding a natural outlet N.N.W. of the sandpit into streamlet No. 1 

 of the section. 



The streamlets Nos. 1 and 2 flow in a westerly direction until 

 intersected by a much larger and longer stream, into which many 

 such streamlets fall. 



Along the line of section at B-B the sands and gravels crop out 

 from under the clay. At such points springs are of frequent occur- 



