﻿J. LeConte — Elevation of the Sierra Nevada. 17& 



were formed not at the time of the birth of this range, but 

 rather during its growth in the Cretaceous, Tertiary, and even 

 at the end of the Tertiary ? 



Evidences of still more recent movements. 



All the fault-movements spoken of above have been going 

 on apparently even to the present time. We have abundant 

 evidence of this in the great Wasatch fault as shown by Gil- 

 bert* and in the faults of the Basin region and especially of 

 Southern Oregon as shown by Kussell.f With every read- 

 justment and increase of fault there is probably an earthquake. 

 The great fault on the eastern side of the Sierra and therefore 

 the elevation of the crest of this range has increased in very 

 recent times and is still increasing. The great Inyo earthquake 

 of 1872 was certainly accompanied and probably caused by a 

 notable (25 ft.) increase of this slip along a distance of 40 

 miles.J This is by far the most probable cause of most earth- 

 quakes. We may conceive forces, of the nature of which we 

 know little, elevating slowly one side of a fissure, usually a 

 mountain range, and the other side dragged up also by adhe- 

 sion, a little way, say 10 to 20 feet, until finally the lower side 

 drops and produces an earthquake. If then the Sierra is still 

 rising, the rivers must be still cutting. The shape of the canon 

 confirms this conclusion. 



Observe, then, that the Post-tertiary rise of the Sierra was 

 not a continental movement merely (for this would not have 

 increased so greatly the slope) ; nor was it orogenic crumpling 

 and up-swelling; but it was elevation of the crest with large 

 increase of the eastern fault-scarp. It is impossible to over- 

 look the connection of this great increase in the height of the 

 Sierra with the progressive desiccation of the Basin region 

 which commenced at this time. 



Contemporaneous Elevation of the west side of South America 

 and subsidence of the mid-Pacific bottom. 



We have thus far spoken only of elevatory movements on the 

 west side of the North American continent ; but a similar move- 

 ment seems to have occurred at the same time and on a still 

 grander scale on the west side of the South American conti- 

 nent also. This is shown by the well known beach lines traced 

 by Darwin up to 1200-1500 feet above present sea level, and 



* History of L. Bonneville, Report of IT. S. Geo]. Surv. for 1880-81, p. 170. 



f History of L. Lahontan, Report of U. S. Geol. Survey, 1881-82, p. 195, and 

 Reconnaisance of Southern Oregon, Report of U. S. Geol. Survey, 1882-83, p. 

 435. 



X Several writers have lately spoken of the readjustment of this fault as the 

 cause of the Inyo earthquake. I believe that the first mention of this was in my 

 article on Origin and Structure of Mountains, this Journal, vol. xvi, p. 101, 1878. 



