ENDLicH.] GEOLOGY SAN LUIS DISTRICT, SECTION B. 333 



curious aud interesting formation of dunes takes place. At the west 

 opening of Mosco Pass a considerable area of ground is covered by 

 bluffs, 500 to 600 feet in beiglit, composed of very fine light-yellow sand. 

 In form these dunes do not vary from the celebrated ones on tlie Baltic 

 Sea, and like those shift onward to the higher land. This phenomenon 

 is a very good illustration of the fact tbat westerly winds prevail to a 

 considerable extent, because none are found on the western side of the 

 valley, and these have selected the very locality where wind would have 

 the fullest sweep through a low pass of a high mountain-range. The area 

 covered by the sand-dunes is about twelve square miles, but the fine sandy 

 soil extends for some miles northward. A fact that finds its exphiuation 

 in the nature of the soil may be mentioned here. More than twenty 

 creeks, heading in the Sangre de Christo range, flow down westward 

 into the valley, but have, however, a short existence, as they are absorbed 

 by their porous beds before running any considerable distance. Some 

 of them run farther in the morning than in the evening, so that, camp- 

 ing on a quite large creek with a i)lentiful supply of water in the morn- 

 ing, by evening it may be necessary to walk half a mile before finding 

 water. The melting of snow in the neighboring mountains and the 

 rain-fall that seems to be quite frequent during the day-time in that 

 region account for the change. 



Ore-deposits. — There are several in section h. A short distance up 

 Grape Creek Canon a deposit of magnetic iron-ore occurs, which is being 

 worked at present. On the western slope of the Sangre de Christo 

 range, not very far from station 19, a large mass of hematite was ob- 

 served, which is not yet worked. In the higher mountains of that range 

 quite frequent indications of silver-bearing lodes were noticed, although 

 none was found. A number of mines were started in 1872 in the Hard- 

 scrabble mining-district, located in the rhyolitic mountains, about three 

 or four miles east of Wet Mountain Valley, near the head of Hardscrabble 

 Creek, the settlement being called Eosita. At the time of my visit 

 there, September, 1873, several mines had been opened, and smelting- 

 works were in course of erection; but I have been informed since that 

 the expectations of the eflicacy aud cheapness of the smelting-process 

 were not fully realized, and discouragement took place. All the lodes 

 are found in a rhyolitic rock, forming a system of regularly-striking 

 l)arallel veins, with a course of about south 25° west, ie., at right angles 

 with the strike of that long, narrow strip of trachorheites running from 

 station 15 to station 83. 



The Senator lode has the above-given strike; is 7 feet wide at the 

 surface aud 12 feet at the bottom of the shaft, which has reached a depth 

 of 40 feet ; dip to the northwest about 120°. The vein can be readily 

 traced on the surface by the quartz-ledge appearing, there. The names 

 ■ of some of the other mines opened on average about to the depths of 20 

 feet are: Virginia ledge, of about 10 feet in width; Gem mine, parallel 

 to the Senator, 6 to 5 feet wide, mostly furnishing galena ore ; the Key- 

 stone, 4 feet wide ; the Steven & Leviathan, with a width of 15 feet ; the 

 Del Korte, 4 feet wide, and several others. A number of quite small veins 

 run parallel with or connect some of those mentioned above, thus form- 

 ing a sort of net-work. The fact of their existing in this rhyolite asso- 

 ciates them with considerable interest ; but although I had expected to 

 find in them some rare minerals that frequently associate in similar 

 places, I was disappointed. As the rhyolite there is of comparatively 

 small thickness, ^^robably not much over 1,000 feet, it seems probable 

 to me that the fissures extend through it, and i)robably continue down 

 into the granite below. Only a few minerals were found in these mines, 

 all of which, however, seemed to contain more or less silver : quartz, 



