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- 
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