PROCEEDINGS 



CALIFORNIA ACADEMY 



SCIEISrCES. 



PETROGRAPHICAL NOTES FROM BAJA CALIFORNIA, MEXICO. 



BY W. LINDGREN, U. S. GEOL. SURVEY. 



During a short viait, in January, 1888, to the northern 

 part of the peninsula of Baja or Lower California, a small 

 collection was made of the rocks occurring near Ensenada 

 de Todos Santos, and along the section from there to the 

 Colorado Desert. A description of the general geology 

 along this route has been published in the Proceedings of 

 the Academy.^ The rocks collected have recently been 

 subjected to a more careful investigation, the results of 

 which are contained in these notes. A few facts regarding 

 the geological structure of the region are here necessarily 

 repeated, while for detailed accounts, maps, profiles, etc., 

 the reader is referred to the paper just mentioned. 



The rocks described may be grouped in five divisions : 



I. Granite and diorite. 



II. Paleovolcanic effusive rocks (quartz- porphyrites). 



III. Neovolcanic effusive rocks (basalt). 



IV. The slate series. 



V. Diabases. 



*Proc. Cal. Acad. Sci., 2ud Ser., Vol. I. Part 2, 188S. 

 2d Ser., Vol. n. Issued June iH, 1889. 



