Features of the Earth's Surface. 465 
convex plateau, it was a north-east and south-west trough. So 
far from being a mountain chain, it was evidently lower than 
the regions east and west of itself At the end of this period 
occurred the Appalachian revolution. The great mass of sedi- 
ments which had been accumulating for so many ages, with their 
included seams of coal, yielded to the horizontal thrust, was crushed 
together, and folded and swelled upward to a height propor- 
tionate to the horizontal crushing. Thus was the Appalachian 
formed—subsequent denudation has made it what it now is. 
It is probable that in the process of the up-pushing of the 
chain (or possibly at a later time) the eastern continental mass 
was diminished by subsidence. 
Sierras.— We have good reason to believe that, at least some 
ortion of the area now occupied by the Rocky Mountains was 
ry land even during the Paleozoic era. To what extent or 
what height we do not know. I shall say nothing of the form- 
ation of this the oldest portion of the North American Cor- 
dilleras, as the history of its formation is little known. I will 
commence with a considerable body of land which certainly 
existed in this region at the beginning of the Mesozoic era. 
Now, during the whole Triassic and Jurassic periods, the region 
now occupied by the Sierras was a marginal sea bottom, receiving 
abundant sediment from a continental mass to the east. At the end 
of the Jurassic, this line of enormously thick off-shore depos- 
its yielded to the horizontal thrust, and the sediments were 
crushed together and swelled upward into the Sierra range. 
All the ridges, peaks, and cafions—all that constitutes the 
grand scenery of these mountains—has been the result of an 
greatly enlarged continent until the end of the Miocene, an 
then it also yielded in a similar manner and formed the coast 
The view that mountain chains are the up-squeezed sediments 
