Recent Exposure of a " Washout " of Strata. 393 



The following is, I think, the sequence of events which are 

 represented in the west end of the section : — First, there 

 was the period of the lowest or first boulder clay, during 

 which the shale which originally lay upon the sandstone, 

 probably to a great thickness, was denuded till only the small 

 patches now visible were left ; then over all — the humph of 

 sandstone and the two patches of shale at each end of it — 

 boulder clay the ground moraine of a great ice-sheet was 

 laid down to a thickness we have now no means of ascertain- 

 ing, but it was probably great. Second, through some change 

 of circumstances during this part of the glacial period, the ice 

 was partially lifted from off the land, and water in the form 

 of rapidly running rivers became possible, and one of these 

 must have run close by the west end of Eedhall Quarry, and cut 

 into the boulder clay, and down through it to the sandstone, 

 exposing anew the truncated edges of the shale, washing 

 away the finer part of the boulder clay, and leaving the 

 rougher parts, the pebbles, the shivers of shale, the slabs of 

 sandstone, the rounded boulders of trap rock, all mixed 

 higgiety-pigglety, as shown in the photograph. There is, 

 however, one regularity in this chaos. All the larger boulders 

 seen in situ rest directly upon the slope of the truncated 

 edges of the shale. The}" took this position doubtless, though 

 sinking by their great weight through the gravelly rubbish 

 till they grounded upon the slope, and did not trundle to the 

 bottom of the slope, because though the gravel was quick as 

 a quicksand is, through being surcharged with water, their 

 weight was not sufficient to push the gravel aside, and over- 

 come at the same time the friction necessarily opposed to 

 their descent. 



The moral to be drawn from the appearances presented by 

 this wash-out is that the glacial period was not simple and 

 uniform in its course, or short in its duration, but was varied 

 and even diverse in its circumstances and lengthened in its 

 time. Taking boulder clay to be moraine matter, the drift- 

 wrack of an ice-sheet then in the first boulder clay, here 

 represented by the denudation of the shale and the vestige of 

 boulder clay which still lies on the top of the slope, we have, 

 first, a great ice-sheet overspreading the whole face of the 



