TRIASSIC. 505 



The fossils that were collected at this point were independently determined by 

 Mojsisovics and J. P. Smith as belonging probably to the Carnien stage of the 

 Upper Triassic of Europe. A second collection of fossils was obtained in greenish 

 sandstones and argillaceous rocks in the western syncline of the Triassic. The 

 authors continue: 



It is proved by the discovery of these fossils that the upper part of the slates of Zacatecas 

 belong to the upper marine Trias. 



A full description of the fauna is given by Burckhardt.'"* 



I 11. SOUTHERN CALIFORNIA. 



The several areas of Triassic rocks southeast of Los Angeles are described by 

 W. C. Mendenhall for this report as follows : 



The Santa Ana Mountains, usually regarded as a southern extension of the Coast Ranges, 

 form a portion of the boundary between Riverside and Orange counties in southern California. 

 The group, which lies for the most part south of the lower course of Santa Ana River and west 

 of the Temescal Wash, culminates in Santiago Peak, 5,680 feet high. Its axis is made up of a 

 series of dark-gray or black slates with minor amounts of interbedded brown sandstones, the 

 whole sparingly intruded by a series of medium acidic dikes and overlain unconformably by 

 remnants of the associated effusives whose aspect is generally that of andesites or slightly more 

 acidic rocks. 



The slates exhibit varying degrees of metamorphism. They usually have a well-developed 

 cleavage, which, however, is generally not sufhciently perfect to obscure the original bedding 

 planes. In general appearance they resemble the Mariposa slate of central California, although 

 as a rule they are less extensively altered. These sediments are the oldest rocks of the mountain 

 range in which they occur. The effusives already mentioned overlie the slates but have been 

 affected by a part of the same metamorphism. 



Both the sediments and the associated effusives have been intruded and slightly altered 

 by great masses of granitic rocks, and this threefold series after a long time interval, represented 

 by an extensive physical unconformity, has been at least partly buried under Cretaceous con- 

 glomerates and shales of Chico aspect that are now entirely unaltered though extensively 

 deformed. These Upper Cretaceous rocks form an encircling outcrop that flanks the dome of 

 older rocks. 



The determination of the age of the slates is based on small collections made in Ladd 

 Canyon, on the south slope of the range, and near the mouth of Bedford Canyon, on its north 

 slope. These collections were examined by Dr. Stanton, who reports as follows on the Bedford 

 Canyon collection: 



"The two Triassic lots, both from the neighborhood of Bedford Canyon, evidently came 

 from essentially the same horizon. No. 230 contains fine specimens of a large species of 

 Rhynchonella of a Mesozoic type and a single specimen of Spiriferina. No. 321 contains the 

 same species as 230 and in addition a plicate form of Terebratula and fragments of crinoid 

 stems. These fossils taken together clearly indicate the Triassic age of the fauna, but in the 

 absence of ammonites and other diagnostic forms it is not possible to determine the exact 

 horizon, although it is probably Upper Triassic rather than older." 



Thus the collections, although meager, seem abundantly sufficient to establish the Triassic 

 age of the slates. Accepting this age, then, as determined, we must assign the later granitic 

 intrusions to the Jurassic or the early Cretaceous. 



The Triassic beds probably extend considerably beyond the area in the Santa Ana Moun- 

 tains where they have been carefully examined. Similar beds are known to occur in Railroad 

 Canyon between Elsinore and Ferris,, and fragmental masses of them apparently caught up in 



