CRETACEOUS AND LATER ROCKS OF PRESIDIO 
AND BREWSTER COUNTIES. 
E. T. DUMBI,E, 
Houston, Texas. 
The developments which have followed the discovery of quicksilver in 
the Terlingna district of Brewster county, Texas, have brought that 
region into some prominence, but, so far as I have seen, there has been 
very little written concerning its geology or that of the area immediately 
east of it. 
The deposits were first brought to my notice during a trip to the 
Trans-Pecos region in the early part of the year 1894, at which time 1 
secured good specimens of the cinnabar for the museum of the Geological 
Survey, although I did not have an opportunity to visit the locality. 
I first announced the discovery of the mineral at one of the regular 
meetings of the Academy. Later the region was examined by several 
mining engineers, and Prof. W. P. Blake described the California mine 
and its surroundings in a paper published in the Transactions of the 
American Institute of Mining Engineers, entitled “Cinnabar in Texas.”* 
This was, I think, the first scientific publication on the subject, although 
there had been numerous references to it in the daily papers and in one 
or two trade journals. 
My first examination of the place was made in company with Prof. 
W. F. Cummins, in August, 1897, and our trip extended as far eastward 
as the base of the Chisos Mountains. Some of the observations made 
will probably be of interest to others who may have occasion to make 
examinations there or elsewhere in the region, as we were so fortunate 
as to hit upon some excellent exposures. 
Starting from Marfa, we drove by way of Alain itos to Alamo de 
Caesario. Securing pack animals and a guide at the ranch, we traveled 
east and southeast, by way of the Bishop mine, about twenty-eight miles ; 
than southwest to the California mine. From this point our route was 
eastward until we reached the coal outcrop on the east of Terlingua 
creek and then southwestward to some new quicksilver prospects of 
Bishop and McGuirk, south of the mine. From this point we returned 
to Alamo de Caesario by way of Fresno creek. 
*Vol. XX V, p. 68. 
