104 MOUNTAINS AND THEIR ORIGIN. 
have been accompanied by a thousand fractures 
and breaks in contrary directions. Such a press- 
ure along so extensive a tract could not be equal 
everywhere ; the various thicknesses of the crust, 
the greater or less flexibility of the deposits, the 
direction of the pressure, would give rise to an 
infinite variety in the results ; accordingly, in- 
stead of the long, even arches, such as character- 
ize the earlier upheavals of the Alleghanies and 
the Jura, there are violent dislocations of the sur- 
face, cracks, rents, and fissures in all directions, 
transverse to the general trend of the upheaval, 
as well as parallel with it. 
Leaving aside for the moment the more baffling 
and intricate problems of the later mountain-for- 
mations, I will first endeavor to explain the sim- 
pler phenomena of the earlier upheavals. 
Suppose that the melted materials within the 
earth are forced up against a mass of stratified 
deposits, the direction of the pressure being per- 
fectly vertical, as represented in 
Figure 2. Such a pressure, if 
not too violent, would simply lift 
the strata out of their horizontal 
position into an arch or dome, 
(as in Figure 3,) and if contin- 
ued or repeated in immediate sequence, it would 
produce a number of such domes, like long bil- 
lows following each other, such as we have in the 
