106 Figure and Comtitiition of the Earth. [Marcli 6, 



Around the margin of the Pacific the mountain chains generally run 

 parallel to the coasts, as if their formation had been the result of a 

 series of incidents in the advance of the continent to enroach upon 

 the ocean. Around the margin of the Atlantic and Indian Oceans 

 the coast generally cuts across the strike of the mountains, as if the 

 sea had advanced to inundate previously existing continents. 



The changes that have taken place in the face of the earth have 

 been ascribed to two kinds of causes : gravitational and tectonic. 

 The gravitational effects are due to changes in the distribution of the 

 earth's mass, producing a shift of position of the oceans. The tectonic 

 changes consist in the formation of mountains, and, possibly, of deeps. 

 Except in so far as they may be incidents accompanying spasmodic 

 but progressive gravitational changes, they are usually associated with 

 the contraction of the earth as it parts with its internal heat, and 

 consequently they are outside the purview of the theory which I have 

 been trying to explain. The gravitational changes have been regarded 

 as a mystery. I hope that this theory may prove to contain the key 

 of the mystery. 



[A. E. H. L.] 



