230 REPORT OF MEETINGS FOR 1902 



as these beds at Siccar Point, amounts to about twelve 

 thousand feet. In Scotland it is impossible to say what 

 the thickness may have been, because the strata are everywhere 

 so much crumpled and disturbed that no reliable estimate 

 can be arrived at. But, whatever it really is, I cannot avoid 

 concluding that the thickness must amount to several thousands 

 of feet. In the Geological Survey Memoir the table on p. 79 

 seems to me to give too small a thickness to the Ludlow 

 Rocks in the Pentland Hills ; and the same remark applies 

 to the Wenlock Rocks of the Central and Southern Belts. 

 This (as I consider it) underestimate does not, however, in 

 any way affect the estimated thickness of the rocks on this 

 horizon in the Lake District. As stated above, there is at 

 least twelve thousand feet of Silurian rocks in that area, 

 counting upwards ftom the horizon represented by the Gala 

 Rocks of the south of Scotland. Nobody questions the 

 correlation of either the uppermost or the 'lowermost strata, 

 when the rooks of the two areas are concerned ; and it follows, 

 therefore, that if the top beds in either area were formed 

 at the same time as those in the other, and if this is true 

 also of the beds at the bottom, it is clear that the rocks between 

 these two platforms must, as a whole, have also been formed 

 contemporaneously with each other. In other words, the 

 one must have taken just as long to form as the other. 



Assuming that this argument is admitted as just, we may 

 briefly notice the history of the Silurian Rocks as a whole, 

 seeing that an understanding of the facts forms an essential 

 feature in part of what is to follow. 



The Silurian rocks represent an accumulation of old 

 sediments — mud, sand, loam, and silt— which were originally 

 part of the rocks of some old continental area. Rain, rivers, 

 and subaerial waste renewed, gradually transferred tho.«e 

 old materials from the land, where they previously existed 

 in the solidified state, to the sea bottom, where, as the land 

 slowly subsided, they were gradually 8i)read out far and wide. 

 The series, almost from top to bottom, shows evidence of 

 quiet and slow accumulation, and I hardly hesitate to make 

 the statement that every foot of even the greywacke — which 

 represents the coarser materials — may well have taken several 

 thousand years to form. 



