328 J. LE CONTE ATLANTIC AND PACIFIC COAST CHANGES. 



of the western slope and the consequent rejuvenescence of the vital energy 

 of the rivers ; the consequent down-cutting of these to form the present deep 

 canons, and the resulting wild, almost savage, scenery of these mountains. 

 So, too, in the history of the Coast range there are two striking epochs. 

 This range also was made by lateral pressure and strata-folding at the end 

 of the Miocene. During the Pliocene, on account of the great continental 

 elevation of that period, this range was powerfully sculptured by erosion ; 

 and deep and wide channels were made by its rivers, the upper courses of 

 which are yet unknown. At the end of the Pliocene, probably coincidently 

 with the great changes in the Sierra, there were here also great lava-flows, 

 and perhaps erogenic movements, which changed the places of the river out- 

 lets. Subsequent continental subsidence submerged the deserted channels, 

 and they remained unknown until discovered by Professor Davidson. 



Thus, rivers are among the best indicators not only of continental move- 

 ments, but also of erogenic changes ; yet they are very differently affected 

 by these changes according to their rate : If the erogenic lifting across the 

 course of a river be slower than the rate of channel-cutting, then the river 

 will cut the mountain to its base and maintain its course. Fine examples 

 of this are found in the plateau region described by Powell. But if, on 

 the contrary, the erogenic dam be lifted mere rapidly than the river can 

 cut — which must always be so in lava-flows, and may be in other cases — 

 then the river will be ponded and the waters may find an outlet some- 

 where else. The rivers of California are examples of this. 



Review. 



Perhaps it will be thought that I have constructed a somewhat elaborate 

 hypothesis en a tee slender basis of ascertained facts. It may indeed be so ; 

 but it is difficult to conceive any explanation of the submarine channels of 

 California except by some such changes as I have suggested. It remains for 

 future investigations to w^ork out the details. The changes in the Sierra and 

 in the upper courses of the rivers are tolerably well known through the in- 

 vestigations of Whitney and others, but those of the Coast range and of the 

 lower courses of the rivers are almost wholly unknown. Attention has only 

 recently been drawn to them by Professor Davidson, and their full geolog- 

 ical significance is now pointed out for the first time. 



It is impossible to conceive a more inviting field for the study of the higher 

 problems of geology than is afforded by the phenomena of the river-beds of 

 California. The main object of this short paper is to direct attention and 

 stimulate investigation. Whether the views presented above be verified or 

 refuted, or whether, as I think more probable, they are corrected and modi- 

 fied by such investigation, it matters little, if so be the truth is established. 



