THE GENESIS OP THE EA.RTH. 7 



ling and folding of the crust visible in great mountain 

 chains, we arrive at a similar conclusion, and also 

 become convinced that the crust has been not too 

 thick to admit of extensive fractures, flexures, and 

 foldings. There are, however, it must be admitted, 

 theories of volcanic action, strongly supported by the 

 chemical nature of the materials ejected by modern 

 volcanoes, which would refer all their phenomena to 

 the softening, under the continued influence of heat 

 and water, of materials within the crust of the earth 

 rather than under it.* Still, the phenomena of vol- 

 canic action, and of elevation and subsidence, would, 

 under any explanation, suppose intense heat, and 

 therefore probably an original incandescent condition. 

 La Place long ago based a theory of the originally 

 gaseous condition of the solar system on the re- 

 lation of the planets to each other, and to the sun, 

 on their planes of revolution, the direction of their 

 revolution, and that of their satellites. On these 

 grounds he inferred that the solar system had been 

 formed out of a nebulous mass by the mutual attrac- 

 tion of its parts. This view was further strengthened 

 by the discovery of nebulae, which it might be sup- 

 posed were undergoing the same processes by which 

 the solar system was produced. This nebular theory, 

 as it was called, was long very popular. It was 

 subsequently supposed to be damaged by the fact 

 that some of the nebulas which had been regarded as 

 systems in progress of formation were found by ini- 

 * Dr. T. Sterry Hunt, in Silliman'a Journal, 1870. 



