EFFECT OF STRUCTURE ON DEFORMATION. 223 



Chico series, and were deeply buried beneath the Chico. As a conse- 

 quence they were subjected to the more rigorous action of deforming 

 forces. The Shasta-Chico series in northern California and Oregon is 

 rarely vertical, and from that angle the clip ranges to nearly horizontal. 

 The gentlest inclinations are in the Chico on the western side and around 

 the northern end of the Sacramento valley, and always miles away from 

 the disturbed lower portions of the same series. 



The geologic date of the disturbance next succeeding the pre-Cretaceous 

 one just referred to is well marked in Oregon, where, as already described, 

 the Tejon is unconformable upon the Shasta-Chico series. Near the 

 unconformable contact the Tejon is not folded, so that the deformation 

 of the Shasta-Chico series, which is conspicuous in that region, took 

 place before the deposition of the Tejon, or about the close of the Cre- 

 taceous. That this deformation was accompanied by upheaval is shown 

 by the absence of Tejon in northern California and part of Oregon. 



This deformation and upheaval appear to have been of great extent 

 to the northward, for the Cretaceous sea which once covered part of 

 Oregon, Washington and a large portion of British Columbia was 

 driven westward by it, in some cases beyond the present limit of the 

 continent; and about this time, according to King, the Wasacht range 

 was uplifted * 



Resume and Conclusions. 



The observations of Dr W. H. Dall have shown that the Wallala beds 

 are a phase of the Chico and belong near the base of those beds, essen- 

 tially in the position assigned to them by Dr White. 



The Chico and Horsetown beds, which were once supposed to be sep- 

 arated by a long interval, are now known to be stratigraphically and 

 faunally continuous, and are the result of an uninterrupted epoch of 

 sedimentation. 



In the same way the Horsetown and Knoxville, which together form 

 the Shasta beds, are shown to lie stratigraphically and faunally contin- 



*The date of the deformation of the Mariposa beds must yet be regarded as an open question. 

 If, as argued by Mr Becker, later by Mr Fairbanks, and finally by Messrs Turner and Lindgren, 

 who have mapped the region, the Mariposa beds are unconformably beneath tin; Chico, their 

 deformation would appear 1" have antedated the deposition of the Shasta-I Ihieo scries, I'm- in the 

 group of strata including lie- Mariposa, Knoxville, Horsetown and Chico beds the argument for 

 faunal and stratigraphic continuity is weakest between the Mariposa and Knoxville beds. The 

 faunal relation of the Mariposa and Knoxville beds, however, is so close, according to Mr Becker, 

 as not to admit of a great physical break hetween them. If one exists it- is possibly local and of 

 limited extent. This might still lie in accord with the facts observed in northern California and 

 < Iregon, where no break has yet been observed within the Aucelta-bearing rocks. 



Numerous observers have called attention to the great mountain-forming epoch about the .lose 

 of the Miocene. During that revolution tic Klamath mountains and tic Sierra Nevada were 

 modified to a large extent. The geologic history referred to in this paper wholly precedes that 

 disturbance. 



