Gordon and Graton — Formations in New Mexico. 391 



the studies of these rocks are yet incomplete and their geo- 

 graphical distribution or extent has not been fully defined, 

 sufficient data are at hand to show that resting upon the pre- 

 Cambrian rocks is a series of beds of a maximum thickness of 

 over 2,000 feet which are representatives of the Cambrian, 

 Ordovician, Silurian and Devonian systems, and that these 

 rocks are present along a belt which crosses Grant, Sierra, and 

 Luna counties, and extends from the east side of the Rio 

 Grande westward beyond the Arizona line and probably con- 

 nects with the similar formations of the Clifton copper dis- 

 trict of Arizona.* The localities where these rocks are best 

 exposed are in the Caballos Mountains near Shandon, in the 

 Hillsboro and Kingston mining districts along the east side of 

 the Black Range, in the vicinity of Cook's Peak and the Florida 

 Mountains, and just west of Silver City. Rocks which unques- 

 tionably belong in the same systems occur in the Georgetown 

 and Lone Mountain mining districts, and probably in the 

 Telegraph district. 



Cambrian. — This system is known to be present in the Bis- 

 bee district in southeastern Arizona, and in Texas, and 

 recently Mr. G. B. Richardson of the IT. S. Geological Survey 

 has found Cambrian fossils in the Franklin Mountains just 

 south of the New Mexico line.f Rocks which have been 

 referred to this system are. known in the Clifton district in 

 Arizona, but heretofore there has been no final proof of the 

 existence of Cambrian formations in northeastern Arizona nor 

 in New Mexico. 



The Cambrian rocks in southwestern New Mexico consist of 

 massive and flaggy quartzites, indurated sandstones, sandy 

 shales, all more or less ferruginous, with occasional beds of 

 siliceous limestone. These strata, which vary from 50 to 

 1,100 feet in thickness, are separated from the underlying pre- 

 Cambrian gneisses and schists by a great erosional unconfor- 

 mity. In the eastern part of the area where these quartzites 

 have been found there appear to be certain well-marked divi- 

 sions of the rocks. The lowest consists of a coarse, dark 

 brown or red ferruginous quartzite, the lowermost beds of 

 which are conglomeratic. As observed in the Florida Moun- 

 tains, this division has a thickness of about 60 feet. Overlying 

 these dark quartzites in some places, and replacing them in 

 others, is a white quartzite, sometimes shaded pink, which varies 

 from a few to 75 feet in thickness. In the Shandon district at 

 the base of the Caballos Mountains this white quartzite is only 

 4 or 5 feet thick, and in places rests directly on the granite. 

 The maximum development of the white quartzite was observed 



*Lindgren. W., Clifton Folio, U. S. Geological Survey, No. 129. 

 f Science, vol. 23, No. 581, p. 267. 



