BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 8 pp. 113-126 February 15, 1897 



EARTH-CRUST MOVEMENTS AND THEIR CAUSES 



ANNUAL ADDRESS BY THE PRESIDENT, JOSEPH LE CONTE 



(Read before the Society December 29, 1896) 

 CONTENTS 



Page 



Introduction 113 



Sources of energy . . ; 113 



Phenomena to be studied 114 



Effects of interior forces 115 



Kinds and grades of earth-crust movements 115 



1 . Ocean basin-making movements 116 



2. Mountain-making movements 119 



3. Oscillatory movements 120 



4. Movements by gravitative readjustments — isostasy 122 



Monoclinal mountain ranges 124 



Conclusions 125 



Introduction. 



sources of energy. 



Nearly all the processes of nature visible to us — well nigh the whole 

 drama of nature enacted here on the surface of the earth — derive their 

 forces from the sun. Currents of air and water in their eternally recur- 

 ring cycles are a circulation driven by the sun. Plants derive their 

 forces directly, and those of animals indirectly through plants, from it. 

 All our machinery, whether wind-driven, or water-driven, or steam- 

 driven, or electricity-driven, and even all the phenomena of intellectual, 

 moral, and social activity, have still this same source. There is one, and 

 but one, exception to this almost universal law, namely, that, class of 

 phenomena which geologists group under the general head of igneous 

 agencies, comprising volcanoes, earthquakes, and more gradual move- 

 ments of the earth's crust. 



Thus, then, all geological agencies are primarily divided into two 

 groups. In the one group come atmospheric, aqueous, and organic 



XVII -Bull. Geol. Soc. Am., Vol. 8, 1896 (113) 



