248 Proceedings of the British Association. 



The conditions necessary for the continuance of the formation of coal 

 were by these disturbances destroyed. The thickness of these rocks 

 probably amounts to 25,000 or 30,000 feet ; the Silurian rocks hav- 

 ing a measured thickness of 10,000 feet, the old red sandstone from 

 4 to 7,000 feet ; the mountain limestone varying from 50 to 2,000 

 feet ; and the coal measures, as ascertained by Mr. Logan, attaining a 

 thickness of from 10,000 to 15,000 feet. This total thickness is not 

 supposed to exist at any one spot, but as each formation required the 

 same time for its deposition as indicated by its maximum thickness, 

 the argument as regards time is the same as if they had all been de- 

 posited at one place continuously. Most of these strata were there- 

 fore consolidated before the disturbances ; and when their great mass 

 and extent is considered, it will be obvious that no small forces could 

 have produced such large effects. It was Mr. Ramsay's opinion that 

 they could only be accounted for by lateral pressure such as would be 

 produced by the " attempt of a solid crust to accommodate itself to 

 a diminishing mass below in a refrigerating sphere." These curves 

 were not produced by forces acting at detached points, the small 

 flexures being but parts of much larger curves affecting the whole 

 country. In illustration, Mr. Ramsay exhibited coloured sections 

 representing the outline of the country and dip of the rocks. From 

 these sections Mr. Ramsay had obtained data for calculating the pro- 

 bable height of the land at various periods. Considering the magne- 

 sian conglomerate as the beach of the new red sandstone sea, the hills 

 of South Wales and the adjacent counties must have attained various 

 elevations, ranging from the level of the sea to at least 15,000 feet 

 high. In a section from Glastonbury Tor to Bristol, the mountain 

 limestone and coal were entirely cut away by the new red sandstone, 

 and oolitic seas. In Glamorganshire and the country towards the 

 Malverns, the coast had been denuded back to the extent in some 

 places of nine miles, and a mass of strata removed sufficient to have 

 formed a deposit of new red sandstone 500 feet thick, over an area of 

 from 200 to 300 square miles. A country possessing mountains of 

 such elevation must have enjoyed every variety of climate, from the 

 tropical to the arctic. The plants of the lias and oolites were sup- 

 posed to be tropical, whilst the insects discovered by Mr. Brodie in 

 the lias were mostly those belonging to a temperate climate, inter- 



