19+ SOUTHERN CALIFORNIA GEOLOGY 



those of the zone of flowage and the former are sup- 

 posed to glide, flow, float, or sink above and within the 

 latter, just as a log of wood or a cake of ice may move 

 about in water. The depth of the zone of fracture, 

 which is also the depth within which faulting move- 

 ments may occur, may probably reach twenty miles. 



The highlands rise as their surfaces are relieved of 

 load by erosion, and as the eroded materials are trans- 

 ported to the margins of the sea by the combined work 

 of sun, wind, clouds, rain and rivers. Correspondingly 

 the sea margins sink as the loads are deposited upon 

 them. 



The sun lifts vast loads of water from the surfaces 

 of the ocean and land — more from the former than 

 from the latter — and the wind transports it as clouds 

 to be deposited in another place as rain and snow load. 

 If you wish to see the work of isostasy, watch the 

 sources, distribution and destinations of the dust of 

 the air, the clouds of the sky and the flood-time sedi- 

 ments of any of our California rivers. 



The latest work of the great geophysicists of the 

 world — Wegener of Austria, Daly at Harvard, Hay- 

 ford and Bowie at Washington, Joy in England — and 

 others — has shown that these great isostatic processes, 

 such as up-and-down and horizontal or lateral drift- 

 ing movements, have played as great if not a greater, 

 part in the deformation of the surface of the earth 

 as has contractional compression. While compressional 

 movements have participated in the geologic struc- 

 ture of California, the drifting and up-and-down float- 

 ing movements have also been most important factors, 

 as testified by the various fault blocks of California 

 which we have described. In fact, lateral compression 



