318 ILLOGICAL GEOLOGY. 



crudely as it was conceived by Hutton, was a temporary 

 generalization needful as a step towards the theory of igne- 

 ous action. 



Since Hutton's time, the development of geological 

 thought has gone still further in the same direction. These 

 early sweeping doctrines have received additional qualifica- 

 tions. It has been discovered that more numerous and 

 more heterogeneous agencies have been at work, than was 

 at first believ€?d. The igneous hypothesis has been ration- 

 alized, as the aqueous one had previously been : the gratui- 

 tous assumption of vast elevations suddenly occurring after 

 long intervals of quiescence, has grown into the consistent 

 theory, that islands and continents are the accumulated re- 

 sults of successive small upheavals, like those experienced 

 in ordinary earthquakes. 



To speak more specifically, we find, in the first place, 

 that instead of assuming the denudation produced by rain 

 and rivers to be the sole means of wearing down lands and 

 producing their irregularities of surface, geologists now 

 see that denudation is only a part-cause of such irregulari- 

 ties ; and further, that the new strata deposited at the botr 

 tom of the sea, are not the products of river-sediment sole- 

 ly, but are in part due to the action of waves and tidal cur- 

 rents on the coasts. In the second place, we find that Hut- 

 ton's conception of upheaval by subterranean forces, has not 

 only been modified by assimilating these subterranean forces 

 to ordinary earthquake-forces; but modern inquiries have 

 Bhown that, besides elevations of surface, subsidences are thus 

 produced ; that local upheavals, as well as the general up- 

 heavals, which raise continents, come within the same 

 category ; and that all these changes are probably con- 

 sequent on the progressive collapse of the Earth's crust 

 upon its cooling and contracting nucleus — the only ade- 

 quate cause. In the third place, we find that beyond 

 these two great antagonist agencies, modern Geology re* 



