the Ea/I/Vs Coiiti'iidioii from Cooling. 211 



face, which have seemed to demand for explanation a liquid in- 

 terior, still remain facts, and present apparently a greater diffi- 

 culty than ever to the geologist. Professor LeConte's views (Am. 

 Journ. Sc. vol. iv.) were offered by him as a method of meeting this 

 difficulty; yet (as he admits in his concluding remarks) the 

 oscillations over the interior of a continent, and the fact of the 

 greater movements on the borders of the larger ocean, were left 

 by him unexplained. Yet these oscillations are not more real 

 than the changes of level or greater oscillations which occurred 

 along the sea-border, where mountains were the final result; 

 and this being a demonstrated truth, no less than the general 

 solidity of the earth's interior, the question comes up, how are 

 the two truths compatible ? 



The geological argument on the subject (the only one within 

 our present purpose) has often been presented. But it derives 

 new force and gives clearer revelations when the facts are viewed 

 in the light of the principles that have been explained in the 

 preceding part of this memoir. 



The Appalachian subsidence in the Alleghany region of 

 35,000 to 40,000 feet, going on through all the Palaeozoic era, 

 was due, as has been shown, to an actual sinking of the earth's 

 crust through lateral pressure, and not to local contraction in 

 the strata themselves or the terrains underneath. But such a 

 subsidence is not possible, unless seven miles (that is, seven 

 miles in maximum depth, and over a hundred in total breadth) 

 of something were removed in its progress from the region 

 beneath. If this something was only vapour or gas, then seven 

 miles of open space must have existed there ; and this could not 

 have been, except through seven miles of local contraction along 

 the region ; but such an open space, if of possible formation, 

 would have been obliterated by catastrophic subsidence, instead 

 of the slow movement that actually took place. And moreover, 

 such open spaces, of no less extent, must have existed, in one or 

 more ranges, underneath all continental borders. This is proved, 

 and at the same time the extreme improbability of their exist- 

 ence demonstrated, by the facts reviewed beyond. 



If the matter beneath was not aerial, then liquid or viscous 

 rock was pushed aside. This being a fact, it would follow that 

 there existed, underneath a crust of unascertained thickness, a 

 sea or lake of mobile (viscous or plastic) rock as large as the 

 sinking region, and also that this great viscous sea continued 

 in existence through the whole period of subsidence, or, in the 

 case of the Alleghany region, through all Palaeozoic time — an 

 era estimated on a previous page to cover at least thirty-five 

 millions of years, if time since the Silurian age began embraced 

 fifty millions of years. 



Q2 



