392 Gordon and Graton — Formations in New Mexico. 



in the Florida Mountains, where the uppermost beds alter- 

 nate with thin beds of limestone, forming a transition to the 

 limestones above. The highest division is a series of beds hav- 

 ing a maximum thickness of 40 feet, composed of dark brown 

 and green, sandy shales and thin-bedded quartzites. These 

 latter rocks are well developed in the Caballos Mountains near 

 Shandon, where in certain layers they contain linguloid shells 

 which have been identified by Dr. Charles I). "Walcott as Obo- 

 lus ( Westonia) stoneanus Whitfield, a form of the Upper 

 Cambrian, found at Newton, N. J., and in the St. Croix sand- 

 stone of Wisconsin. In no one place were all three divisions 

 observed, and it may be the white quartzite is but a local phase 

 of one of the other divisions. 



Near Silver City these rocks have a thickness of nearly 1,100 

 feet. They consist mostly of quartzites of dark red, brown or 

 black color due to iron stain, which contain three beds of cherty 

 limestones 30 to 75 feet thick, and near the top and near the 

 bottom a thin band of shale ; a few feet at the very base is a 

 conglomerate. 



Ordovician. — A series of limestones, for the most part 

 massively bedded and having a maximum thickness of 1,200 

 feet, rests conformably upon the Cambrian rocks. The thinly 

 bedded cherty members of the lower portion of this series sug- 

 gest resemblance to Abrigo limestone of the Bisbee district,* 

 which is Middle Cambrian, but some poorly preserved organic 

 remains found about 100 feet above the quartzite in the Silver 

 City section are regarded by Mr. E. O. Ulrich of the U. S. 

 Geological Survey as belonging certainly in the Lower Ordovi- 

 cian. At this place, where the upper limit is not definite, the 

 limestones considered to be Ordovician are about 770 feet thick, 

 consisting at the bottom of 265 feet of cherty limestone over- 

 lain by 185 feet of alternating narrow bands of limestone and 

 chert, and succeeded by about 330 feet of gray or pinkish, fine- 

 grained, siliceous limestone. 



In other localities the limestones of the lower portion of 

 the series are notably crystalline, and near the axis of the 

 Black Range at Kingston and in the Carpenter district they 

 are essentially marbles, often mottled blue and white. In 

 these crystalline beds no fossils have been found. The upper 

 members are in part composed of thin cherty beds. A stratum 

 of quartzite from 3 to 5 feet thick is present in places near the 

 top of the series, but is not persistent. 



Fossils are fairly abundant in the upper part of these lime- 

 stones. Corals are most common, and at Silver City brachio- 



*Ransome, F. L., Prof. Paper, IT. S. Geol. Surv., No. 21, p. 33. 



