Features of the Earth’s Surface. 471 
In regard to fissure-eruptions, nothing but general contraction 
and a squeezing out of liquid matter can account for the 
Whitney* thinks this squeezing out the result of subsidence 
of areas on either side of the mountain chain. I confess I do 
not understand the mechanics of this. Of course it could not 
be subsidence by weight, for this is inconsistent with the princi- 
ples of hydrostatic pressure. It could only be by a concave 
bending of a stiff crust pressing on a fluid interior; but this 
over a large area is impossible, for the reasons already given in 
the early portion of this paper. Besides, pressure on a general 
interior liquid would be propagated equally to every portion of 
the interior surface of the solid crust, which would therefore 
yield not necessarily in a contiguous part, but at the weakest 
point wherever that may be. In fact, if we admit the interior 
fluidity of the earth, the mechanics of igneous agencies is sur- 
rounded with insuperable difficulties on every side. The more 
we try to arrive at clearness the more the difficulties seem to 
accumulate. ‘ 
The theory which I have just presented accounts, it seems 
me, for all the principal facts associated in mountain chains. 
This is the true test of its general truth. It explains satisfae- 
torily the following facts. 1. The most usual position of 
tain chains near continental coasts. ~ 2. When there are several 
ranges belonging to one system, the ranges" have usually been 
formed successively coast-ward. 3. Mountain chains are masses 
of immensely thick sediments. 4. The strata of which moun- 
the cleavage planes being usually llel to the mountain 
_ chain. 5. The strata of mountain chains are usually affected 
with metamorphism, which is great in proportion to the height 
of the mountains and the complexity of the foldings. 6. Great 
* Mountain building, etc., p. 90. 
