41G PROF. J. F. BTiAKF ON TFIE MONIAN AXJ) 



from Wentnor to Lydham, dipping at a gentle angle from the Cam- 

 brian rocks on which they rest. 



Many changes doubtless took place in this district during Devonian 

 times, but these changes did not result in its submergence, since 

 the Old Red Sandstone is only found in the south. More probably 

 they resulted in its greater elevation ; and the main fault, which 

 did not exist during Silurian times, may now have been produced. 

 The area of deposition was then transferred to the north ; and from this 

 direction came the later Coal-measures to abut naturally against the 

 old rocks with an outline produced by denudation. In the same 

 direction followed the Termian. then the Trias, which envelops the 

 still remaining peaks of the ancient rocks, by Haughmond and the 

 "Wrekin ; and even the Lias at Whitchurch is tending towards the 

 same point ; and none of these rocks have any representatives south 

 of the Longmynd. Finally, even in the Glacial epoch, there appears 

 to have been no submergence. The lower valleys on all sides are 

 filled with Drift, but there is none of it on the surface of the hills ; 

 only on the northern side, whence the boulders travelled, do we find 

 it, as it were, forced up-hill in the direction of its course. Here the 

 boundary rises from a level of about 700 feet near Lebotwood to as 

 much as 1050 feet on Picklescott Hill, descending to about 600 feet 

 again to the east of Church Pulverbatch. In this direction a few 

 boulders have even reached the summit of the hills, as at Church Pul- 

 verbatch itself and on Cothercott Hill. The boulders, as far as I have 

 seen, are all of northern origin. Xone of them are of the Longmynd 

 rocks, and the ice which thus pushed forward up a hill has left its 

 striae on the rocks of Charlton Hill, at a height 340 feet above the 

 sea. 



We thus perceive that the ancient rocks of the Longmynd have 

 been exposed to denudation ever since the middle of Lower-Cambrian 

 times, and the valleys we now see cutting across the vertical strata 

 of the hardest and most insoluble grit, and carrying water remarkable 

 for its clearness and purity, are the end result of its work. 



§ VL General Conclusions. 



We are now in a position to determine how far my suggestion 

 that the Longmynd rocks are not Cambrian, but Upper Monian, was 

 correct. It is obvious that here, where the succession of the later 

 rocks is so well made out, we are in the most critical locality for 

 settling the existence or not of a system of ordinary stratified rocks 

 subjacent to the Cambrian. 



In the first place, in the face of the fact that the rocks hitherto 

 comprised under the term Longmynd are not homogeneous, but 

 consist of two distinct and unconformable portions, every state- 

 ment made up to this time regarding them must be modified. Thus 

 it is no longer permissible either to say the Longmynd rocks are 

 Upper Monian or to give one name, sucli as that of Longmyndian, 

 to the whole. Again the proofs that have hitherto been given that 



