180 Lee — Lowe?' Paleozoic Rocks of Central New Mexico. 



Art. XXII. — Notes on the Lower Paleozoic Rocks of Central 

 New Mexico /* by Willis T. Lee. 



The lower Paleozoic rocks are exceptionally well exposed 

 in the Caballos Mountains of central Sew Mexico. Gordon 

 and Gratonf refer to them in a description of the lower 

 Paleozoic formations in New Mexico, bnt attention is confined 

 by these writers principally to other parts of the territory, and 

 the occurrence, especially of the Cambrian and the Ordovician 

 •formations, in the Caballos Mountains, as well as their relations 

 to each other and to the overlying rocks, are of sufficient inter- 

 est to warrant the more definite statements contained in this 

 paper. 



The Caballos Mountains form one of the small mountain 

 groups of central JSTew Mexico and occur west of the town of 

 Engle between the Rio Grande and the Jornado del Muerto. 

 The northern part of the mountains consists of a faulted block 

 tilted to the east and the sedimentary formations outcrop in 

 the precipitous western face. The lower part of the slope 

 consists of granite, above which occur the Cambrian, Ordovi- 

 cian and Carboniferous rocks as shown in the following section 

 measured about three miles north of Shandon, a mining camp 

 on the Rio Grande. With the Cambrian and Ordovician of 

 this section are correlated similar rocks observed in other 

 parts of the Pio Grande Yalley. 



A few species of fossils were found in the Cambrian sedi- 

 ments, and these have been identified by Dr. C. D. Walcott of 

 the Smithsonian Institution. Possils collected from the Ordo- 

 vician rocks have been examined by E. O. Ulrich of the 

 United States Geological Survey, and the quotations given 

 in the paper are from his written report. The Ordovician 

 fossils are not well preserved and specific identification is 

 difficult. 



A thickness of 1000 feet or more of the granite is exposed 

 in the cliffs. The rock is massive and coarsely crystalline, 

 although schist and gneiss occur in some places. Its surface 

 was apparently eroded in early Cambrian time to a nearly 

 level plain upon which the sedimentary rocks were deposited. 

 The coarse-grained and, in some places, conglomeratic quartz- 

 ite at the base of the Cambrian grades upward into the green 

 shale, in which the Cambrian fossils occur in great abundance 

 at several horizons, some close to the basal quartzite, others 

 near the top. 



* Published by permission of the Director of the U. S. Geological Survey, 

 f Gordon, C. H. and Graton, L. C, Lower Paleozoic Formations in New- 

 Mexico, this Journal, xxi, pp. 390-395, 1906. 



