The Evolution of the Sciences 



distributed over all the continents, and the 

 ocean covers, perhaps, a greater number, as 

 almost all dredgings made in the Pacific have 

 brought up traces of volcanic tufas. And if to 

 these centres of activity are added all extinct 

 volcanoes, which are studded over the face of 

 the earth like boils scarcely healed, one recoils 

 from the number of separate cavities and lakes 

 required to account for their existence. As 

 M. de Lapparent points out the entire Pacific 

 and all the surrounding land would have to be 

 considered to rest on a lake of lava. Under 

 these conditions it is difficult to imagine the 

 existence of solid walls between such liquid 

 masses; it is difficult to understand how any 

 differences of chemical constitution or of tem- 

 perature could have raised walls of this nature 

 within a mass originally entirely liquid. 



On the other hand the general trend of these 

 phenomena can be interpreted by the assump- 

 tion that the folds of the crust have formed; 

 within the globe deep intercommunicating 

 cavities, which subdivide the earth into suffi- 

 ciently independent regions for a disturbance 



occurring in any one of them to leave the re- 



148 



