Physical Geography. 87 



that these Lower Silurian strata were being deposited. 

 The only sign of pre-existing land, is found on the west 

 coast between Cape Wrath and Loch Torridon, where 

 the Llandeilo beds lie alike unconformably on the 

 Cambrian and Laurentian strata. This proves, that 

 when the lowest Llandeilo beds began to be depo- 

 sited, the underlying rocks formed the eastern margin 

 of a territory, of which probably our Outer Hebrides was 

 only a part, but how far it may have stretched westward 

 it is impossible to say. However that may have been, 

 it seems certain that long before the uppermost strata 

 of the Lower Silurian rocks of Scotland were deposited, 

 these fragments of an older land, which are still pre- 

 served on the west, had been long submerged and 

 buried under the accumulating piles of the Silurian 

 strata. That even then an extensive land lay not 

 far off is certain, for the extent and great thickness of 

 the Lower Silurian rocks affords a measure of the 

 amount of waste of a pre-existing territory, the partial 

 and gradual destruction of wnich, by all the agencies 

 of denudation, provided mechanical sediments wherewith 

 to form thousands of feet of Silurian strata of mud and 

 sand, first consolidated, and long after metamorphosed 

 into quartzite, gneiss, and mica-schist. This land may 

 have occupied an area now covered by the Atlantic ocean. 



