250 PROCEEDINGS OF THE CALIFORNIA 



at its base. The strata are more or less inclined, and the lower beds are very 

 much contorted and disturbed. The rocks referred to the Trias extend from 

 Soyopa to San Javier ; but they are developed on a more extensive scale 

 between San Antonio de la Huerta and Los Bronces, forty-two leagues north- 

 east of Guaymas. The Triassic rocks form a chain of high and rugged mount- 

 ains extending from south-southeast to north-northwest. The isolated mining 

 districts of Tecoripa and San Marcial (between Los Bronces and Guaymas) are 

 in the same formation ; it also crops out from under the stratified volcanic rocks 

 at the Puuta de Agua, between San Marcial and Guaymas. The metalliferous 

 greenstones aud porphyries, previously noticed, form the nucleus around which 

 the Triassic beds have been upheaved. These beds are seen near San Javier 

 and Los Bronces, two mining towns which are situated on greenstone, but which 

 skirt the foot of a small ridge of feldspathic porphyry, much less elevated than 

 the metamorphic rocks themselves. They are also seen overlying granite, near 

 the Cerro Colorado, between Soyopa and Los Bronces, and south of Tecoripa. 

 The Cerro de la Nahuila, the highest point but one in the district, lies southeast 

 of the Sierra de Mazatan. There are three principal divisions of the Triassic, 

 which occur in the following order, the first mentioned being the lowest : 



j Quartzites and clay slates ; 

 I Black, jaspery schistose layers ; 



or, where the rocks are less altered : 



j Black clay shales with beds of coal ; 

 ( Argillaceous sandstones. 



2. Quartzites, in great thickness. 



3. Heavy beds of conglomerate. 



The interstratified clay shales and grits of the lower member, crop out in 

 several places along the Canada de Santa Maria, at the bottom of the ravines 

 below Los Bronces. Here, there are three or four beds of good anthracite coal, 

 with a considerable number of well-preserved plants occurring in the associated 

 clay shales, both above and below the coal. 



[A portion of these plants were referred by me to Dr. Newberry for examin- 

 ation, and he has given the following list of them. 1. Strangeriles rnagnifolia, 

 Rogers ; Trans. Assoc. Am. Geologists, p. 306, PL xiv. A species occurring 

 in the Trias (?) of Virginia and North Carolina. 2. Pecopteris fakatus, Em- 

 mons ; Geol. of N. Car., PI. iv, fig. 9. The specimens are too imperfect to 

 decide on the identity of this plant with Saccopteris germinans. ? 3. Pecopteris 

 bullatus, Bunbury ; only in fruit ; nervation obscure ; identity not certain, but 

 very probable. 4. Otozamites Macombii, Newb. At top of "red beds" or 

 "gypsum formation," at the base of the Cretaceous rocks, copper mines near 

 Abiquiu, New Mexico. There is no doubt about this species, and it forms an 

 important connecting link. ? 5. Pterozamites decussatits, Emmons ; specimens 

 very imperfect. 6. Pecopteris, n. sp. ; a very neat and peculiar species as yet 

 undescribed. It may be the same as one badly figured by Emmons (PI. II, fig. 1.) 



