178 Proceedings of the Royal Physical Society. 



north and east, in the interior, and in the west and south. 

 In Asia, again, they occupy wide areas in the Indian 

 Peninsula ; they are well developed in the Himalaya, while 

 in China and the mountains and plateaux of Central Asia, 

 azoic rocks, which are probably of Archaean age, are well 

 developed. The crystalline schists, which cover extensive 

 tracts in Australia and in the northern island of New Zealand, 

 have also been referred to the same age. Thus all the world 

 over, Arch«an rocks seem to form the surface of the ancient 

 continental plateau upon which all other sedimentary strata 

 have been accumulated. And in every region where Palaeozoic 

 rocks occur, we have evidence to prove that at the time these 

 last were formed vast areas of the old continental plateau 

 were under water. 



The geological structure of the Palaeozoic tracts of Europe 

 and America has shown us that, during the protracted period 

 of their accumulation, and notwithstanding many oscillations 

 of level, the land-surface continued to increase. The same 

 growth of dry land characterised Mesozoic and Cainozoic 

 times, — the primeval depressions that traverse the con- 

 tinental plateau, became more and more silted up, and the 

 sea eventually disappeared from extensive regions which it 

 had overflowed in Palaeozoic ages. This land-growth, of 

 course, was not everywhere continuous. Again and again, 

 throughout wide tracts, depression was in excess of sedi- 

 mentation and elevation. Even at the present time, broad 

 tracts of what was once dry land are submerged. But the 

 simple fact that the younger fossiliferous strata do not 

 extend over such wide areas as the older systems, is suffi- 

 cient proof that our land-masses have all along tended to 

 grow, and to become more and more consolidated. 



Eeference has already been made to the remarkable fact 

 that no abysmal accumulations have yet been detected 

 amongst the stratified rocks of the earth's crust. Ordinary 

 clastic rocks, such as shale, sandstone, and conglomerate — 

 altered or unaltered, as the case may be — form by far the 

 largest proportion of our aqueous strata, and speak to us 

 only of shallow waters. It is true that some of our lime- 

 stones must have accumulated in moderately deep clear seas, 



