PRIMAL ENERGIES 



and in the cavity thus formed the pent-up molten 

 lava finds relief. These lava cisterns or pockets are 

 sometimes uncovered by the process of erosion. 

 The Henry Mountains in Utah are all laccolites. 

 One of them, Mount Hillers, has a volume of about 

 ten cubic miles. Much of the overarching sedimen- 

 tary strata still covers it. Geologists read the evi- 

 dence of a similar formation called a "sill" on the 

 west side of the Hudson in New Jersey, forming the 

 Palisades. The lava worked like a giant mole up 

 through and then beneath the Triassic sandstone, 

 lifting the strata up and arching them over a large 

 area. During the millions of years that have elapsed 

 since that time, the layers of superincumbent sand- 

 stone have been worn away so that now one sees a 

 wide, smooth, gentle slope of basaltic rock covered 

 by a very thin coat of soil. As one goes by on the 

 train, one sees where the workmen of a stone-crush- 

 ing plant have cut into the slope and uncovered the 

 junction of the two kinds of rock, one born of water, 

 and one born of fire. The igneous rock sits squarely 

 upon the level sandstone, like a row of upright 

 books standing upon a shelf. I never pass the place 

 but that I want to stop the train and get out and 

 have a close look at the precise spot where this son 

 of Vulcan sat down so heavily and so hot upon his 

 brother of the sedimentary deposits. 



Probably no two chapters of the earth's history 

 differ more than those of the two sides of the Hud- 



173 



