18 Proceedings of the Royal Physical Society. 



It will be observed that while the English subdivisions in 

 the diagram show a sequence of strata actually traced through 

 various districts, the Scottish strata do not similarly repre- 

 sent such a natural classification. Care must therefore be 

 taken, lest in an attempt after apparent uniformity of classi- 

 fication of these latter strata the actual physico-geographical 

 relations exhibited in the rocks themselves be set aside. 

 A classification denoting the succession which actually may 

 thus be traced in the coalfields of Scotland would be of far 

 closer approximation to the truth than the one given above. 

 Were such an inquiry entered into, it is highly probable 

 that it will be found that the whole Scottish coal strata are 

 not synchronous in geological age with the English series, 

 but are parallel only with one or two of its lowest members. 



According to the diagram, the total thickness of the 

 Lancashire strata is 14,200 feet, whilst that of the Lothians 

 is only 6400 feet. The mountain limestone is one magni- 

 ficent pile of calcareous matter in England, until it borders 

 the confines of Yorkshire ; but the equivalent series in Scot- 

 land, though containing one or two insignificant limestone 

 beds, is in reality a succession of sandstones, coals, and shales. 

 The Scottish analogues of the two intermediate English 

 groups are confessedly imperfect or absent ; while even the 

 true Scottish Coal Measures but poorly represent the magni- 

 ficent English members of the series in thickness or position. 



Of course it will be remembered that even the smallest 

 subdivision represents an enormous lapse of time ; a lapse 

 of time, so great, indeed, as to allow of the most extensive 

 changes in sea and land, and a persistence in such physical 

 revolutions utterly alien to any of our notions founded on 

 historic time. The cycles of change in a geologic aeon are 

 not at all to be measured even by the overturning of dynas- 

 ties and kingdoms in our human epoch. Consequently the 

 Scottish carboniferous strata may represent a period of phy- 

 sical change very distinct from those chronicled by the 

 English strata. The state of land and sea may have repeat- 

 edly changed, — physical conditions requisite for the depo- 

 sition of peculiar minerals may have been in action and 

 ceased at different epochs of the great Carboniferous seon. 



