TilE CENTURY'S PROGRESS IN GEOLOGY 



present, according to Professor Dana's estimate, as three 

 to one. 



Towards the close of this Paleozoic era the Appalachian 

 Mountains were slowly upheaved in great convoluted 

 folds, some of them probably reaching three or four 

 miles above the sea-level, though the tooth of time has 

 since gnawed them down to comparatively puny limits. 

 The continental areas thus enlarged were peopled dur- 

 ing the ensuing Mesozoic time with multitudes of 

 strange reptiles, many of them gigantic in size. The 

 waters, too, still teeming with invertebrates and fishes, 

 had their quota of reptilian monsters ; and in the air 

 were flying reptiles, some of which measured twenty-five 

 feet from tip to tip of their bat-like wings. During this 

 era the Sierra Nevada Mountains rose. Near the east- 

 ern border of the forming continent the strata were per- 

 haps now too thick and stiff to bend into mountain 

 folds, for they were rent into great fissures, letting out 

 floods of molten lava, remnants of which are still in evi- 

 dence after ages of denudation, as the Palisades along 

 the Hudson, and such elevations as Mount Holyoke in 

 western Massachusetts. 



Still there remained a vast interior sea, which, later 

 on, in the Tertiary age, was to be divided by the slow 

 uprising of the land, which only yesterday that is to 

 say, a million, or three or five or ten million years ago 

 became the Rocky Mountains. High and erect these 

 young mountains stand to this day, their sharp angles 

 and rocky contours vouching for their youth, in strange 

 contrast with the shrunken forms of the old Adiron- 

 dacks, Green Mountains, and Appalachians, whose low- 

 ered heads and rounded shoulders attest the weight of 

 ages. In the vast lakes which still remained on either 



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