OP SAISTTO DOMmao. ' ■ 187 



In one of his excavations I found an approach to a vein sti'ucture, in a seam of quartz 

 and slate, the vein swelHng and narrowing very irregularly. In the quartz are nests 

 of pnrple sulphuret of copper, some of them as large as one's fist, and little streaks and 

 threads of the mineral are not rare. On crushing and washing a sample of this quartz 

 I found a minute trace of gold. The country rock is a greenish gray claystone often 

 much cross-fissured and in places slightly talcose. In one place it is dark gray and is 

 spotted with small yellowish grains. It is about on the strike so far as can be deter- 

 mined "between Cobre and the copper deposits of the i^^igua at Monte Mateo. ' ' - 



Although the slates on the ISTigua are so highly metamorphosed that it is next to 

 impossible to discover their dips over a great, part of the distance, yet from the al- 

 most continuous exposures along the canon of the river the section is one of the best 

 that occurs through these rocks. I have traversed the entire width of the nietamor- 

 phic belt many times and while the main features are easily distinguishable have 

 almost always arrived at different conclusions about the dips of the jaspery slates 

 between Tablasas and Pomiel. There is no question but that they all dip more or less 

 southward, but in one or two places the strike twists around to the north and south 

 and the dip is nearly vertical. My main conclusions are confirmed by the limestones 

 which retain their bedding well marked, and in a few places between the two above 

 named points I believe I have found the true position of the slates, though I have been 

 obliged to reject the greater part of my observations as based on too uncertain data. 

 The slates have regular systems of fissures often extending entirely throughout an 

 outcrop, and frequently so regular as to appear certainly the stratification ; but othei's 

 equally well-marked cross these in entirely diflferent directions, and not rarely several 

 of these systems occur together. Another source of confusion exists in the color- 

 ation of the rock. It is usually a dark bi'own or green, but bands of color, a foot or 

 more wide, often extend entirely across an exposure. This looks as if it originated 

 in some trifling difierence in the original constitution of the beds, now consolidated 

 into a homogenous mass, but closer examination develops the fact that these bands 

 are not of uniform width, they sometimes end abruptly, taper out, or widen and en- 

 close masses of the predominant color of the surrouiiding rock; in short they possess 

 all of the irregularity of mineral veins. At first I was misled by them, l^ut on meas- 

 uring a great number I found that they must have had their origin in some other 

 cause than the original stratification. 



The eruptive rocks extend southward to just below the mouth of Jamei Creek, 

 their eastei'n margin, a nearly noi'th and south line, cutting across the heads of most 

 of tlie tributaries of the finina. On the southern niai'gin they are often of unusuallv 



