256 REPORT OF MEETINGS FOR 1902 



thickness of mud, sand, loam, and silt was spread out in 

 even layers far and wide, pile upon pile, over the sea bottom. 

 It was the strata formed during this Silurian Period which, 

 after being consolidated and very much affected by later changes, 

 subsequently saw the light as the great pile of convoluted 

 greywackes and argillites out of which the Peeblesshire hills 

 were at a later time to be carved. 



The event of most importance that followed the formation 

 of the rocks was their subsequent upheaval and crumpling, 

 which the reader who is curious in such matters will find 

 more fully described in a paper dealing with the Club's 

 excursion to Old Carabus and the Siccar Point, to which I 

 must refer for details of what followed ; for the history of 

 that part of Scotland coincides in almost every particular with 

 the history of this, so far as this chapter is concerned. 



Suffice it to say that after the Silurian rocks had been 

 much crumpled and disturbed, and had undergone enormous 

 denudations, first the Caledonian Old Eed was laid down upon 

 their edges; then these were wasted away and, afterwards, the 

 Upper Old Red Sandstone, followed by a thick pile of Carbon- 

 iferous rocks, took its place over the old surface formed of 

 the Silurian rocks. Then the whole compound (so to speak) 

 was folded, faulted, and denuded again. Next came the New 

 Red Sandstone, which was spread out in very unequal thicknesses 

 over nearly the whole of the south of Scotland, and was 

 followed by the marine and widely distributed Jurassic rocks. 

 These, in their turn, underwent denudation, and an extensive, 

 and very even, plain was formed, upon which in later times 

 the Cretaceous rocks were spread out. 



It is, I think, this old pre-cretaceous floor, since upheaved 

 and slightly bent, and then re-exposed by the removal of 

 the rocks which formerly lay upon it, which forms the summit- 

 plain of the Peeblesshire hills. 



Now, it was long after the Cretaceous rocks were formed 

 that the upheaval took place which lifted the plain upon 

 which the Cretaceous rocks lay to something like the level, 

 averaging something over 2000 feet above the Ordnance Datum, 

 which this summit plain occupies at present. 



I think that when the rivers of the district began to flow 

 none of the rocks which at present form the hills were exposed. 



