BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 2, pp. 323-330 March 16, i891 



TERTIARY AND POST-TERTIARY CHANGES OF THE 

 ATLANTIC AND PACIFIC COASTS ; 



"WITH A NOTE ON 



THE MUTUAL EELATIONS OF LAND-ELEYATION AND ICE-ACCU- 

 MULATION DURING THE QUATERNARY PERIOD. 



BY JOSEPH LE CONTE. 



(Rend before the Society Decemhei- 31, 1890.) 



CONTENTS. 



Page. 



The Atlantic Coast and its Changes 323 



Physical Geography of the Coast 323 



Coast Changes 324 



The Pacific Coast and its Changes 324 



Physical Geography 324 



Orogenic History 325 



Changes in Rivers 326 



Comparison of Eastern and Western River Beds 327 



Brief History of the Rivers and Ranges of California 327 



Keview 1 328 



Note on the Mutual Relations of Land-Elevation and Ice- Accumulation during 

 the Quaternary Period 329 



The Atlantic Coast and its Changes. 



Physical Geography of the Coast. — It is well known that the North Amer- 

 ican continent is bordered on both sides by a submarine plateau sloping 

 gently seaward until it attains a depth of about 100 fathoms, and that from 

 this 100-fathom line the bottom drops off rapidly into deep water. This 

 submarine plateau may be regarded as a submerged coastal plain, and its 

 margin as the true boundary between the continent and the ocean-basin, 

 i. e., as the submerged continental margin. 



It is also well known that on the eastern coast this submarine plateau is 

 trenched with deep submarine troughs running out from the mouths of the 

 great rivers to the submerged continental margin and there opening into 

 deep water. The best known of these submarine channels are : (1) One 



XLVIII-RuLL. Geol. Soc. Am., Vol. 2, 1890. (323) 



