

MOUNTAIN-MAKING. 795 



Wahsatch Mountains was 60,000 feet thick, according to King. The 

 beds for the Appalachians were not laid down in a deep ocean, but in 

 shallow waters, where a gradual subsidence was in progress ; and they 

 at last, when ready for the genesis, lay in a trough 40,000 feet deep, 

 filling the trough to the brim. 



It thus appears that : — 



2. Epochs of mountain-making have occurred only after long in- 

 tervals of quiet in the history of a continent. 



Mountain-making closed the Archaean era. After the end of the 

 Archaean, or the beginning of the Primordial, the first period of dis- 

 turbance in North America of special note was that at the close of 

 the Lower Silurian, in which the Green Mountains were finished ; 

 and if time from the beginning of the Silurian to the present included 

 only forty-eight millions of years, the interval between the beginning 

 of the Primordial and the uplifts and metamorphism of the Green 

 Mountains was at least (judging from the relative thickness of the rock 

 deposits, p. 381) twenty millions of years. The next epoch of moun- 

 tain-making on the Atlantic border was after, or in the course of, the 

 Devonian in Nova Scotia and New Brunswick ; on the above basis, it 

 occurred thirty millions of years from the beginning of the Primor- 

 dial. The next epoch of disturbance was that at the close of the Car- 

 boniferous era, in which the Alleghanies were folded up ; by the above 

 estimate of the length of time, thirty-six millions of years after the 

 commencement of the Silurian. The next on the Atlantic border 

 was that of the displacements of the Triassico- Jurassic sandstone and 

 the accompanying igneous ejections, which occurred before the Creta- 

 ceous era — at least five millions of years, on the above estimate of 

 the length of time, after the Appalachian revolution. These numbers 

 are mentioned here, not as even an approximate estimate of the real 

 length of the interval, but only of relative lengths, and especially to 

 make apparent the fact that these intervals were very long. 



On the Pacific border of the continent there was mountain-making 

 at the close of the Jurassic, when the Sierra Nevada was made ; and, 

 over the coast region, at the close of the Miocene Tertiary, when, ac- 

 cording to J. D. Whitney's latest Report (on the Auriferous Gravels), 

 the Cretaceous and Miocene formations of the coast region were to- 

 gether folded and made into mountains. But for the Rocky Mountain 

 region, no proof has yet been reported of any epoch of disturbance 

 between the end of Archaean time and the close of the Cretaceous, at 

 which the Wahsatch and Uintah Mountains were made ; and, more 

 than this, the evidence indicates that through all that long interval, 

 covering nine tenths of all geological time after the Archaean era had 

 closed, the rocks of those mountains were being laid down in consecu- 



