478 G. B. Richardson — Paleozoic Formations. 



typically a massive gray magnesian limestone which contains 

 the same fauna in both regions. In the El Paso area the 

 formation is about 1000 feet thick, the lower 100 feet of 

 which is characteristically arenaceous and weathers brownish. 

 A distinctive feature of the middle portion of the formation 

 is the presence of thin connected nodules of brown chert 

 arranged in irregular streaks parallel to the bedding. This 

 limestone lies apparently conformably on the Bliss sandstone, 

 but, as already stated, in the central part of the Franklin 

 Mountains the Bliss sandstone is locally absent and the El 

 Paso limestone rests directly on pre-Cambrian (?) rocks with a 

 basal conglomerate varying up to 20 feet thick composed of 

 rounded pebbles of rhyolite porphyry in a calcareous matrix. 

 In the Van Horn quadrangle the El Paso limestone does not 

 contain the cherty layers that are characteristic of the middle 

 parts of the formation in the Franklin Mountains, and 50 

 feet above the base of the formation a thin bed of white sand- 

 stone is present. In this region there are indications of an 

 unconformity at the base of the limestone marked by a slight 

 undulatory contact between the El Paso and Yan Horn 

 formations. 



Mr. Ulrich reports that the fossils obtained from the El Paso 

 limestone in both the El Paso and Van Horn quadrangles rep- 

 resent essentially the same Beekmantown fauna. Most of the 

 species are undescribed, but all are of unmistakable types. 

 The more characteristic forms are the following: 



Calathium, sp. nov. (coral-like sponge), Maclurea ? sp. nov. 

 The small horn-like opercula are very common. The shell 

 itself is of the type of M. oceana Billings. Solid siphuncles 

 of endoceratoid cephalopod, evidently a close ally of Camero- 

 ceras brainardi. Besides these there are a number of less 

 easily recognized small gastropods. 



Montoya Limestone. 



The Montoya limestone also has been recognized by its 

 stratigraphic position and fossils in both of the quadrangles. 

 This limestone contains two distinct Ordovician faunas, the 

 Richmond and Galena, and on paleontologic grounds it is 

 desirable to separate the two, but the small thickness of the 

 formation, only about 250 feet, and the scale of the maps will 

 not admit of it. 



Fossils characteristic of the Galena occur in the lower part 

 of the Montoya limestone, the zone being commonly marked 

 in the El Paso quadrangle by massive dark-colored limestone 

 containing little or no chert. The upper part of the limestone 

 is prevailingly gray, but some of the beds are almost white 



