Genth.] -^4: [March 18, 



their occurrence. They are all from the Sierra de Catatlan, in the State 

 of Durango, and comprise the following : 



No. 1. Ore from Mina del Diablo. "Clace 1% Cristal." 

 " 2. " " " " " Clace 2». 



" 3. " " " de San Antonio. 

 ■" 4. Washings received from Mr. W. Schlemm. 

 " 5. Ore from Mina Varosa. 

 " 6. Stream tin ore, marked "Superior de Placer. " 



The central body of the Sierra de Catatlan, in which the mines which 

 have furnished these ores are siluateil, consists of quartz-porphyry, which, 

 in some places, is traversed, in a net-like manner, by small veins of tin 

 ores. About one mile from the Mina del Diablo doleritic rocks occur. 



Nos. 1 and 2. Tlio vein of the Mina del Diablo has been traced for 

 about one mile in length, it has a thickness of from eighteen inches to 

 two feet, is almost perpendicular, and perfectly separated from the 

 porphyry by argillaceous selvedges. It consists of a decomposed white 

 clayey material, containing druses of quartz with tin ores. In a pocket 

 was found a white clay in which crystals and crj'stalline aggregations 

 (No. 1), and also finer ore (No, 2), were intermixed. On wasliing, this 

 pocket yielded about 54 per cent of clean ore, the crystals and crystalline 

 aggregations were picked out from a large quantity of clay, and weighed 

 about C50 grms, yielding nearly 50 grms in well defined shape. 



This occurrence is completely exhausted ; the deeper and harder por- 

 tions of the vein contain tin ores, but not any of these peculiar crj'^stals. 

 A qualitative examination of the crystals as well as of tl'e finer ores, 

 although different in form, showed the composition of mimelite, mixed 

 with more orlesscassiterite, small quantities of porphj^y, quartz, hematite, 

 clay, etc. Many interesting specimens of cassiterite, mostly of a red 

 variety, were picked out from the mimetite crystals and crystalline 

 aggregations ; they all showed such an unusual appearance that it was de- 

 sirable to obtain a larger quantity from the second-class ore. The finer 

 portion was separated by a sieve of 16 meshes to the square inch, and 500 

 grms. of the sifiings treated with hydrochloric acid until all the mimetite 

 was dissolved. The residue was treated with Thoulet's solution, which 

 gave in the heavier portion a little over 15 grams of cassiterite with a few 

 crystals of hematite, while the lighter consisted principally of quartz, 

 with little feldspar, fragments of porphyry, kaoline, etc. 



A fuller description and analyses of the various minerals and varieties 

 from the Mina del Diablo will be given in the sequel. 



No. 3. The San Antonio Mine has furnished in a seam, six inches in 

 thickness, a length of ten feet, and a height of eight feet, an ore in the 

 form of pulverulent or very friable, earthy yellowish masses, with darker, 

 somewhat more ferruginous streaks. There were only a few very small 

 particles of the red variety of cassiterite present, most of it being of a 

 yellowish color. A partial analysis gave : 



