38 Proceedings of the Ohio State Academy of Science 



and ocean basin, taken in connection with the shrinking of the 

 earth following cooling and condensation, gives the starting point 

 of geological processes. The earth is divided into continental and 

 oceanic segments, the former lighter, the latter heavier, the 

 former making one-third of the earth's volume, the latter two- 

 thirds. The sinking of the larger heavier oceanic segments 

 crowds the continental segments. This results in a squeezing up 

 of the continental segments, of which we find evidence in the 

 repeated uplift of the land surface. The folded and faulted 

 mountain ranges, which occur principally along the borders of 

 continents, are due to the lateral thrusts and readjustments along 

 the borders of the segments. 



The continental platforms have therefore been described as 

 positive elements, the oceanic basins as negative elements. With- 

 in each, on a smaller yet absolutely large scale, positive and nega- 

 tive elements occur. The continental platform, does not act as a 

 unit, if we consider detail. There have been areas of repeated 

 uplift, positive elements, of which one of the best known is the 

 area of crystalline rocks along the Atlantic sea-board known as 

 Appalachia. Through geological history it has been a land area, 

 frequently renewed by uplift, almost always subjected to erosion. 

 While to the west of it the Appalachian trough existed during 

 Paleozoic time as a negative element, an area of repeated sub- 

 sidence and of deposition. And yet both, in a large way, were 

 but parts of the larger unit, the continental platform. This sub- 

 division of the positive continental areas into positive and nega- 

 tive elements of a lower order is a direct inference from the 

 field studies. 



But these views which I have summarized are new. Le 

 Conte in his Elements of Geology had a beautifully clear and 

 adequate state of the immediate conditions which led to the 

 formation of a folded mountain range like the Appalachians. 

 But his theory did not apply equally well to ranges like the Sierra 

 Nevada, which is a great block of the earth's crust tipped up 

 along its eastern border, nor to ranges like the Big Horns and 

 Black Hills, cut out of broad, more or less flat-topped up-bow- 

 ings of the crust, nor to block uplifted plateaus. Le Conte as- 



