lviii REPORT OF THE STATE GEOLOGIST. 



also refer a series of rocks of a similar character and trend found in 

 the Trans-Pecos country, in the vicinity of Eagle Flat and the Carrizo 

 Mountains, the areal extent of which is as yet entirely unknown. • 



This system, beginning in a condition of shallow seas, shows by its 

 manner of stratification, the layers of basic materials that occur in it, 

 and the local differences in sections, that it had a vacillating border. In 

 the Llano Series eruptive rocks were interbedded near its close; but 

 during the Packsaddle epoch deeper water prevailed, probably until the 

 upheaval which gave the rocks of this entire series their present north- 

 south trend. This system closes the first great era of the geologic his- 

 tory of this region — a period marked through the three eras we have 

 described by conditions of depositions, interrupted and broken by great 

 eruptions of igneous matter, which appear to-day interbedded, or as in- 

 trusions, or as smaller and larger dykes. According to the materials of 

 which they were composed and conditions of eruption, they are now 

 granites of various kinds, certain basic (hornblendic, etc.) schists, feld- 

 spars, quartz, etc.; and after their final elevation the materials which 

 erosion has taken from the rocks of these systems has always formed a 

 part in the formation of the systems that overlie them. 



Perhaps there is no place where there is a stronger illustration of the 

 necessity for the careful study of the structural geology, as a basis for 

 accurate economic work and determination, than is found within the 

 region covered by the rocks of the three great systems just described. 

 For years this Central section has been held forth as a rich mineral re- 

 gion. The evidence of the occurrence of ores is plainly discernible by 

 any one examining the district. The surface indications are plentiful, 

 and often a single blast will show lumps and nodules of less or greater 

 size of grey or peacock copper. In spite of this, and although much 

 money has been spent in prospecting, no success has been obtained in 

 mining, because the real relations of the ore bearing veins to the general 

 geology were not understood on account of the various complications 

 caused by the different uplifts, and could not be ascertained without 

 more detailed work than had ever been given it. The search was, there- 

 fore, in most cases a haphazard one, and nothing practical came of it. 

 The facts gathered by the survey greatly alter this, and we are now able 

 to present them in such manner as will greatly assist the practical miner 

 in his work. 



We have definitely associated the various veins of silver, copper, lead, 

 iron, and manganese, each with its proper series of rocks, and the care- 



