534 Murchison 1 s Silurian System. 



erected, from its isolated position in the centre of a valley 

 formed by old red sandstone, might at first be supposed 

 to have been torn from a gap with which it corresponds at 

 Cwrt-a-bard'dh, and precipitated down the shelving escarp- 

 ment upon the surface of the old red sandstone ; an infer- 

 ence, Mr. Murchison remarks, that would not appear extra- 

 vagant in this region of violent disturbance. Mr. Murchison 

 however offers another explanation. It is evident, he says, 

 from the beds on either side of the valley, as well as from 

 those on which the castle stands, that the whole of the 

 district has been violently b en up by those move- 

 ments of elevation to which the coal basin of South Wales 

 was subject. Earthquakes and subterranean forces suffi- 

 cient to raise the circular escarpment of this coal field 

 could not have acted, Mr. Murchison thinks, on such large 

 accumulations of sedimentary matter without occasioning im- 

 mense transverse openings or channels. On the supposition 

 that such operations were going on for a long time before the 

 deposits in question were raised above the waters, powerful 

 must have been the submarine currents set in action by these 

 changes of level ! How must they have affected the bottom of 

 the sea, and how deeply must such currents have channelled 

 out the hollows into which they were deflected ? By all 

 these operations Mr. Murchison conceives the vallies of de- 

 nudation on the skirts of the South Wales coal field have 

 been determined, deepened, and increased; and we may here 

 remark, that the explanation applies equally to the dry sinu- 

 ous vallies in all lofty regions, as the Alps, and the Himalaya, 

 and the Khasya mountains. 



We have dwelt longer on the details given by Mr. Mur- 

 chison regarding the different members of the coal forma- 

 tion, from the very great importance of the subject in India. 

 It is however difficult for the student to acquire a knowledge 

 of any branch of natural science by reading alone ; all that 

 the best books can do, is to put him in the way of recording 



