endlich.] SAN JUAN MINES. 231 



Proceeding to the head of Cunningham Creek, the volcanic rocks are 

 seen only as forming the crests of ridges, while the main drainage runs 

 over metamorphic rocks. Station 17, near the head of the creek just 

 mentioned, is located on gneiss, and may be regarded as one of the out- 

 posts of the metamorphic area already mentioned. From there the Hue 

 of outcrop extends east and southeast on the one side, west and south 

 on the other. Local accumulations of mica or quartz change the lith- 

 ological character of the rock, and the appearance of chlorite in it gives 

 rise to a continuation of the metamorphic area to the southeast as chlo- 

 rite schist, the rock composing the lower portions of the Cunningham 

 walls, and containing a number of ore-veins. Farther down on the 

 Animas, where these metamorphic rocks should be expected to crop out, 

 within a few miles below Baker's Park, on the Animas Canon, we find 

 nothing but volcanics. Along either side of the river, from Cunning- 

 ham Gulch downward to the point just given, volcanic rocks appear to 

 form the entire mass in view. Although the lower portions of the rocks 

 exposed probably do not belong to No. 3, it is very difficult to identify 

 them with any one of the underlying groups, and they must be referred 

 to a position near to or in intimate connection with No. 4. Owing to a 

 large quantity of debris in Arastra Gulch, the majority of lodes thus 

 far discovered have been claimed at an elevation of more than 1,000 

 feet above the creek. At no point in that gulch have I observed crop- 

 ping out of metamorphic schists, although I have reason to believe that 

 they really do underlie the volcanic material. This suspicion is based 

 upon the character of the Little Giant ore, which contains chlorite and 

 none of the minerals mostly found in the trachorheites. Prospecting 

 has also been done farther down the river, but as my time was limited, 

 I bad no opportunity of visiting any of the lodes there located. 



The conditions on the west side of the Animas appear to be of a more 

 simple character, the metamorphic rocks not reaching over in such a 

 manner as to crop out, although at some depth they may probably be 

 found. It is possible that considerable erosion took place before the 

 volcanic flows invaded the regions, and before the lodes were formed — 

 a view which is supported by the fact that near the head of Cunning- 

 ham Gulch a light blue to white limestone crops out, which, according 

 to its lithological character, must be referred to the Upper Silurian or 

 Lower Devonian of that region, no fossils having been found that might 

 establish its age beyond a doubt. 



The metamorphic rocks of that region, in which stations 23, 25, and 

 38 are located, show many variations. From a pure quartzite they pass 

 over into micaceous schists, into gneiss, and at some points into a coarse- 

 grained granite. Schists occur that contain the characteristic staurolite 

 twins, scarcely to be distinguished from some eastern localities. Nu- 

 merous small and large veins of white quartz traverse these schists, 

 showing sometimes slight indications of ore. 



In speaking of the lodes of the region under consideration, it is nec- 

 essary to state that but little work bad been done upon them ; that 

 there are existing no mines of any appreciable depth ; and that but 

 very little time could be spent upon their inspection. These facts ex- 

 clude the possibility of deciding with any considerable degree of accu- 

 racy the character of the ore-bodies at any greater depth. It was nec- 

 cessary to make almost all studies on the immediate surface ; and as from 

 a series of such observations no law can be derived exhibiting the ratio 

 of development as compared to the depth, it stands to reason that none 

 definitely to be relied upon can be here given. The geological char- 

 acter of the veins under consideration is a very interesting oue, and I 



