Story of the Mississippi- Missouri. — Claypole. 371 
tant outbreaks. Seminary Ridge, where the Confederate army 
was stationed, and the Little and Gray Round Tops are merely 
bosses of dolerite whose hardness has enabled them to sur- 
vive the softer beds that formerly overlay them, while the 
famed Devil's Den is a valley of erosion lying between them 
and heavily strewn with their wreckage. 
During this long lapse of time mutterings of coming dis- 
turbance were not unheard in the west. The regions of the 
Rocky mountains, so long at peace, began to feel the thrusts of 
a mighty earth-force. And though the geology of the western 
district is yet far from being worked out we know that during 
the age in question the range of the Sierra Nevada was ele- 
vated and that about the same date the Wahsatch and the 
Uinta ranges came into being. These were but forecasts of 
what was about to occur and heralded the second great revolu- 
tion in the geological history of the continent. 
But the Cretaceous age passed away without, so far as we are at 
present aware, any very great disturbances in the North Ameri- 
can area. Yet we are certain that there must have been changes 
of no small extent in other parts of the globe for at the end 
of this era there occurred the widest extinction of species that 
geology has yet revealed. So far as North America and Europe 
are concerned very few animals or plants passed up from the 
Cretaceous into the Tertiary deposits. Into the cause of this 
significant fact we need not enquire here. It was probably the 
result of great changes in the distribution of land and sea. 
We have ample indications of this in the disappearance of the 
waters from the long cliannel already described running from 
the gulf of Mexico to the Arctic ocean. In this had been suc- 
cessively laid down the Triassic, Jurassic and Cretaceous 
strata. But at the end of the latter age the channel became dry 
land and never since that day has the ocean invaded the 
heart of the continent. 
The geological history of the western states was in fact a 
repetition of that of the east. Through all the secondary or 
mesozoic era the greater part of that area was in a condition 
of slow and intermittent subsidence like that of the eastern 
border during the eras of paLneozoic time. But soon after the 
close of the Cretaceous age this subsidence was arrested and 
a counter movement set in. Before the Tertiary era had far 
advanced vast areas of the western country began to emerge 
