276 I^' William B. Carpenter [Jan. 23, 



of whose theoretical views will show how entirely they harmonize with 

 the conclusions drawn from inquiry into the present conditions of the 

 great Oceanic areas : — " As the globe has cooled from fusion, it 

 has been all through time a contracting globe ; and this contraction 

 of the crust has been the chief agency in determining the evolution 

 of the earth's surface-features, and the successive phases in its long 

 history." " The crust which should form over a melted sphere, as it 

 cooled, would have the size the sphere had at the time. As it thick- 

 ened downwards by the continued cooling, the added portions would 

 contract ; and this would occasion lateral pressure through the crust, 

 which would increase as the cooling and thickening continued." 

 Keasons are adduced by Professor Dana for the belief that the forma- 

 tion of the solid crust would not go on at the same rate all over the 

 sphere ; but that some portions of the surface would solidify into a 

 layer several miles in thickness, whilst over other large areas the 

 sui'face would still be liquid or in a state of only incipient solidifica- 

 tion. The level of the latter would be gradually lowered by the con- 

 traction of the cooling mass beneath ; and the crust of these depressed 

 areas would constitute the Ocean-floors, whilst the elevated areas, rising 

 by abrupt sides from their borders, would remain as Continental 

 plateaux. The study of the geological structure of the North Ameri- 

 can continent leads Professor Dana to the conclusion that " in its very 

 inception, not only was its general topography foreshadowed, but its 

 great mountain-chains appear to have been begun, and its great inter- 

 mediate basins to have been defined. The evolution of the grand 

 structure-lines of the continent was thus early commenced, and the 

 system thus initiated was the system to the end. Here is one strong 

 reason for concluding that the continents have always been continents ; 

 that while portions may have at times been submerged some thousands 

 of feet, the Continents have never changed places with the Oceans" 



The progressive shrinkage of the internal mass, as its cooling 

 proceeds, must produce a falling inwards of the crust formed around 

 it ; and the lateral pressure thus exerted through the whole crust will 

 necessitate a yielding somewhere. The lateral thrust is likely to be 

 exerted most advantageously from the floors of the depressed Oceanic 

 areas against the sides of the elevated Continental plateaux ; and this 

 is borne out by the fact that " the continents have mountains along 

 their borders, while the interior is generally low " ; and that " the vol- 

 canoes of the continental areas are mostly confined to the sea-borders." 

 Further, " the largest and loftiest mountain-chains, greatest volcanoes, 

 and other results of uplifting and disruptive force, characterize the 

 borders of the greatest oceans, showing that the lateral pressure from 

 the direction of the oceans was approximately proportional to the ex- 

 tent of the oceanic basins." Thus, in North America the lofty and 

 massive AUeghanies are raised up on the Pacific side ; the minor 

 Appalachian chain on the Atlantic. In South America, the great 

 chain of the Andes, with its lofty volcanoes, is in like contrast with 

 the comparatively insignificant mountains of Brazil. So, on the Euro- 



