1922] Hudson: Geology of the Cuyamaca Region of California 189 



J. P. Smith, in his paper on "The comparative stratigraphy of 



the marine Trias of western America, ' ' says : 



Dr. H. W. Fairbanks has discovered in the Santa Ana Eange, Orange County, 

 California, some fossiliferous limestones with pelecypods resembling Daonella 

 and a traehyostracan ammonite not generieally identifiable. These beds prob- 

 ably represent the Lower Trias, but the fossils are too scanty for a definite 

 opinion to be based on them.s 



The results of the work of W. C. Mendenhall have been published 

 in the "Index to the Stratigraphy of North America." 9 He reports 

 that the axis of the Santa Ana Mountains 



is made up of a series of dark -gray or black slates with minor amounts of inter- 

 bedded brown sandstones, the whole sparingly intruded by a series of medium 

 acid 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 sufficiently perfect to 

 obscure the original bedding planes. In general they resemble the Mariposa 

 slate of central California, although as a rule they are less extensively altered 



Both the sediments and the associated effusives have been intruded and 

 slightly altered by great masses of granitic rocks, and this three fold series after 

 a long time interval, represented by an extensive physical unconformity, has 

 been at least partly buried under Cretaceous conglomerates and shales of Chico 

 aspect 



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 



Dr. Stanton decided, in the case of the Bedford Caiion collection, 

 that the fossils are clearly Triassic. No mention is made of the 

 determination of the Ladd Canon collection, but presumably it also 

 indicated a Triassic age. 



Quoting Mendenhall further : 



The Triassic beds probably extend considerably beyond the area in the Santa 

 Ana Mountains where they have been carefully examined. Similar beds are 

 known to occur in Eailroad Canyon between Elsinor and Perris 



Merrill in a recent publication applied the name "Julian Group" 

 to the crystalline schists of San Diego County. He says : 



The metamorphic formations are mica schists, slates, quartzites and lime- 

 stone, the first being especially well exposed near Julian and the latter occur- 

 ring in small areas at several points. These metamorphic rocks, from their 

 structural position and lithologic characters, may be regarded as probably equiv- 

 alent to the Calaveras group described in the Mother Lode Folio of the U. S. 

 Geological Survey and will be here designated as the Julian group. Their exact 

 age is uncertain. 10 



s Smith, J. P., Proc. Calif. Acad. Sci., ser. 3, vol. 1, 1904, p. 352. 

 t> Willis, Bailey, U. S. Geol. Surv. Prof. Paper, 71, pp. 505-506, 1912. 

 io Merrill, F. J. H., "Geology and mineral resources of San Diego and Im- 

 perial counties," Calif. State Min. Bur., 1914, p. 12. 



