490 EMMONS AND MERRILL — SKETCH OF LOWER CALIFORNIA. 



can be piaced upon them. Our knowledge of the topographical struc- 

 ture is mainly based on the descriptions of the few intelligent travellers 

 who have traversed various parts of the peninsula. 



The only important publications with regard to the geology of Lower 

 California are : 



1. That of W. H. Gabb,* paleontologist of the California Geological 

 Survey, who in 1867 traversed the entire peninsula from cape Saint 

 Lucas to San Diego on muleback, crossing it ten times during the trip. 



2. That of W. Lindgren,t who in June, 1888, spent a few weeks in the 

 vicinity of Todos Santos bay (Ensenada) and the mountains to the east 

 of it. 



SoQie geological notes are also found in the reports of the Mexican 

 boundary and Pacific railroad surveys, the latter by W. P. Blake. Re- 

 ports on mines in the southern part of the pemnsula sometimes contain 

 geological data, but they are rarely accessible, and at best have seldom 

 more than a local bearing. 



The original observations on which the present paper J is founded 

 were made by Mr Merrill during a fortnight's trip, in July, 1892, from 

 San Quentin on the west coast, in latitude 30° 30', to the deposits of Mex- 

 ican onyx, about 150 miles distant, a little south of latitude 30 and near 

 the eastern or Gulf coast ; and by Mr Emmons during a stay of somewhat 

 longer duration, mainly at the property of the New Pedrara Onyx Com- 

 pany above mentioned, including overland trips thither Irom San Quentin, 

 and from the quarries across the peninsula to the west coast between 

 Bluff and Canoas j^oints, in latitude 29° 30'. 



Since that time there have appeared papers by Mr H. W. Fairbanks § 

 and Professor A. C. Lawson|| upon the geology of southern California 

 which contain facts that have an important bearing upon the structure 

 of the adjoining peninsula. 



Physical Structure. 



The peninsula of Baja California is a narrow strip of broken moun- 

 tainous land extending roughly from 22° 50' to 32° 30' north latitude, 

 about 775 miles long and from 35 to 70 miles in width, with a general 

 northwest and southeast trend parallel to the larger orographic features 



* J. Ross Brown : Min. Res. of the U. S. for 1867, Wash., 1S68, p. 630. 



t W. Lindgren : " Notes on the Geology of Baja California-Mexico." Proc. Cal Acad. Sci., 2d ser., 

 Yol, i, 1888, p. 173. Ibid., vol. ii, January, 1889, p. 1. Ibid., vol. iii, April, 1890, p. 26. 



Jin this paper the petrographical determinations wrere made by Mr Merrill. Mr Emmons is 

 alone responsible for the general structural deductions, in determining which he has made free 

 use of Mr Merrill's field-notes. 



g"The validity of the so-called Wallala beds as a division of the California Cretaceous." Am. 

 Jour. Sci., vol. xlv, June, 1893, p. -173. 



II "The P.»st-Pliocene Diastrophism of the Coast of Southern California." Bull. Univ. Cal., vol. i, 

 no. 4, December, 1893, p. 115. 



