THE ADIRONDACK MOUNTAINS 4I 



Grenville strata are now very frequently not in horizontal position 

 as when they were deposited under the sea. On the other hand, 

 there is no known evidence that the Adirondack Grenville strata 

 were ever severely folded or compressed as has been the case in 

 many mountain ranges, as the Appalachians, for example. j\Iany 

 broad belts of Grenville are known to be only very moderately 

 folded to almost horizontal ; numerous masses, large and small, are 

 merely tilted or domed ; while very locally the strata sometimes are 

 contorted or sharply folded. The structural relations are, therefore, 

 best explained as having been the result of slow, irregular, upwelling 

 of the more or less plastic molten masses, probably under a moder- 

 ate compressive force or lateral thrust in the crust of the earth, 

 whereby the strata, previously disturbed little or none at all, were 

 simply broken up or tilted or domed. In many places the evidence 

 is perfectly clear that the tilting of the Grenville strata was 

 directly due to the up-push of the intrusive rocks. Locally, where 

 masses of Grenville were caught between two bodies of upwelling 

 molten rock, the strata were sometimes twisted or sharply folded, 

 this having been especially true of the relatively very plastic lime- 

 stones. It appears to have been literally true that the Grenville 

 strata were irregularly floated on a vast body of molten rock, the 

 latter in many places either having arched up or broken through the 

 strata. In other words, the Grenville strata, as well as the great 

 intrusives, were not subjected to real mountain-making pressure in 

 the crust of the earth whereby the rocks were thrown into a series 

 of great folds, as has happened in many mountain regions of the 

 world. 



We can not even state the approximate height of those very 

 ancient Adirondacks. Also we are utterly in the dark as to the 

 character of the topography and the direction of the drainage lines. 

 The fact that thousands of feet of material have been removed by 

 erosion, thus exposing the present rocks to view, does not neces- 

 sarily imply that the mountains at any time had a very great height 

 because it is possible that, while elevation slowly progressed, 

 material was steadily removed by erosion. All our knowledge of 

 later and better known mountains, however, leaves little doubt but 

 that those ancient x\dirondacks were notably higher than those of 

 today. 



Later Prepaleozoic history. The profound erosion of the very 

 ancient Adirondacks extended through some millions of years of 

 the later Prepaleozoic and even into very early Paleozoic time, but 



