C. A. White—Age of Coal in the Rio Grande region. 19 
counties; and in Mexico, in the States of Nuevo Leon and 
Coahuila. By certain local geologists and mining experts, 
whose reports have fallen under my observation, a part of these 
coals have been referred to Carboniferous age, and others to 
_ Triassic* age. From personal examination in the field, extend- 
ing over a large part of the region in question, and an exam- 
ination of fossils which have been collected by different 
personst from strata associated with the coals, I am satisfied, 
however, that none of them are of earlier than late Cretaceous 
age. 
In some cases the coal of this region is worthiess for practical 
use, but in others it is of good quality; all of it having the 
general characteristics of the coals which are obtained from the 
Laramie and Fox Hills formations in Colorado, Utah and 
Wyoming. From the data and observations just mentioned I 
do not hesitate to refer all the known coal of the region under 
consideration to one or the other, or both, of those formations. 
In the region of the Lower Rio Grande these two formations 
appear to be as intimately associated with each other as they 
are to the northward. Their strata are so similar in general 
character that it is usually difficult to define a plane of demark- 
ation between them, and in the absence of paleontological 
evidence it is often difficult or impracticable to distinguish the 
one from the other. 
I have at present no evidence of the presence of the Laramie 
formation in Webb and Maverick counties, Texas, the coal 
which has hitherto been found there belonging to the equiva- 
lent of the Fox Hills Group of the Cretaceous period. The 
mines at Santa T’omas, some forty miles above Laredo, and 
those seven miles above Eagle Pass, are the principal ones on 
the Texas side of the river. The equivalent of the latter coal 
is also found on the’ Mexican side, a few miles from Piedras 
Negras, opposite Eagle Pass. 
From data furnished by Mr. Gardiner, I also learn that both 
the Laramie { and Fox Hills formations exist on the Mexican 
side of the Rio Grande, in the northern part of the State of 
Nuevo Leon and the adjacent eastern portion of the State of 
Coahuila, and that both formations are coal-bearing there. 
On the occasion of a late journey in Coahuila, I found both 
these formations to be well developed in the region which is 
*Tn an otherwise important article by W. H. Adams, M.E.; in the Trans. 
Inst. Mining Engineers, vol. x, pp. 270-273, entitled Coals in Mexico, Santa Rosa 
District, he refers the coal-bearing rocks there to Triassic age; and those at Eagle 
Pass to the Permian, both of which references are erroneous. 
+The collections referred to were made by Mr. James T. Gardiner, of New 
York, Mr. W. F. Cummins, of Dallas, Texas, and Mr. R. T. Hill, of the U. 8. 
Geological Survey. 
{See this Journal, III, vol. xxv, pp. 207 et seq. 
