372 



University of California. 



[Vol. x. 



of American geologists to whom geology is so deeply indebted for 

 certain broad views and far-sighted generalizations, which inspirit and 

 expression recall the wide regions and clear atmosphere in which their 

 authors worked. The result of this review was to bring to the 

 writer's attention many serious objections to the hypothesis as it 

 has been held by probably the greater number of American geolo- 

 gists, and to cast doubt upon views in regard to sedimentation and 

 subsidence which he had hitherto been rather disposed to entertain. 

 It seemed desirable to eliminate this element of uncertainty as far 

 as possible by the study of some particular area to which the theory 

 of isostasy would seem to be applicable; and for this purpose the 

 Great Valley of California is peculiarly fitted, in that it is an exten- 

 sive area, possessing very definite boundaries, in which subsidence 

 has apparently gone on step by step with sedimentary loading. It 

 is, moreover, a physiographic feature of more than ordinary interest, 

 which, as a whole, has never been made the subject of geological 

 investigation. There are, it is true, many obstacles in the way of a 

 complete discussion of the valley at the present time, owing to the 

 imperfect knowledge possessed of certain portions of it, and the 

 lack of any accurate map of the whole area. Accordingly the fol- 

 lowing discussion must be to a certain extent tentative, although it 

 is believed that the information at present available is enough to 

 serve as a basis of treatment, and it is hoped that with growing in- 

 terest in physiography more attention will be given to the gathering 

 of data bearing upon the later history of, on the whole, the most 

 important physiographic feature of the state. 



In the following pages it is proposed to give (i) a description of 

 the Great Valley as it is to-day, (2) an outline of the geological evo- 

 lution through which it has arrived at its present form, (3) an 

 account of the development of the so-called "doctrine of isostasy " 

 as a working hypothesis, (4) a discussion of the applicability of this 

 hypothesis to the Great Valley, and (5) a more general discussion 

 of the theory of isostasy, with illustrations drawn from other regions 

 of elevation or subsidence. 



PHYSIOGRAPHY OF THE GREAT VALLEY. 



General Features and Subdivisions. — The Great Valley of Cali- 



