ORIGIN OF MO UNTA IN RA NGES. 559 



of the present Appalachian crest. The sediments along this mar- 

 ginal sea-bottom increased in thickness during Cambrian, Silurian, 

 Devonian and Carboniferous (with some changes of Physical 

 Geography, but without greatly changing the line of sedimenta- 

 tion) until 40,000 feet thickness was reached. Such thickness, of 

 course, could not be attained without pari passu subsidence. We 

 have additional evidence of this in shallow water fossils and even 

 shore marks at many levels in the series. At the end of the coal 

 period, when 40,000 feet had accumulated, the increasing softening 

 along the line caused it finally to yield to horizontal thrust ; the 

 whole mass of strata was crumpled together and swelled up along 

 the line of sedimentation and the Appalachian Range was born. 

 The same forces which caused its birth continued to cause its 

 grotvtli for a long time. Subsequent erosion has sculptured it into 

 its present form, but has not exposed its granite core. The crest is on 

 the east or landward side, as we should expect, and the overfolds 

 are to the west or toward the sea of that time. This is perhaps 

 the most typical example we have. 



2. Sierra. — If it were not for a subsequent movement so late 

 as the beginning of the Quaternary, which greatly modified its 

 form, the Sierra too would be a typical range. During the whole 

 Palaeozoic and the greater part of the Mesozoic the place now 

 occupied by the Sierra was the eastern marginal bottom of the 

 Pacific, receiving sediments from a continental land-mass in the 

 present Basin region. The shore line changed somewhat at the 

 end of the Palaeozoic, but the Sierra region maintained a sea 

 bottom position. At the end of the Jura, when an enormous 

 thickness had accumulated, the increasing softening of the crust 

 determined a yielding to lateral thrust and consequent formation 

 of the range. Subsequent erosion has completely removed the 

 strata from the crest and exposed the granitic core as an axis r . 

 This axis is here also on the landward side, and the overfolds are 



"Sierra granite is not Archaean as has been asserted by some, nor does it all ante- 

 date the birth of the range. This is proved (1) by the gradation traceable between 

 slates and granites, and (2) by the fact stated by Whitney, by Fairbanks, and byDiller 

 — that the granite in many places penetrates the slate as veins. 



