SECTIONS OF THE NEW ALMADEN. 321 



which crops oat on Mine Hill. To this series belong the various Santa Rita 

 "labores" exhibited on the southern part of the section, and the series of 

 winzes extending from the Santa Rita to the 1,400-foot level of the Randol 

 shaft, sliowing here and there a small stope, was sunk along the course 

 of the same fissure. The main stopes on this section are on the north fis- 

 sure, which divides the great body of rock forming the hanging country 

 of the south fissure from the region north of the mine. 



Another view of the two fissures is shown on Atlas Sheet XII, where 

 they are intersected by an east and west vertical plane. To the right ap- 

 pears the south ore channel, including the O'Brien, Don Federico, and other 

 bodies ; to the left is the north fissure. 



Existence of two principal fissures. — The cxisteuce aud positiou of thc two fissurcs 

 are not so evident and clear as would appear from the foregoing notes. The 

 ore bodies lie upon complex curved surfaces. The result is that no vertical 

 plane intersects both fissures at right angles throughout, and no single sec- 

 tion affords indubitable evidence of two fissures. Views similar to those 

 shown in the sections might be given of two channels along a single, doubly 

 curved surface. Could one but represent the fissures by contours, the en- 

 tire structiu'e would be shown in three dimensions and would not be ambig- 

 uous. A certain approximation to this result can be reached. As was 

 mentioned above, the fissures are marked by clay seams or altas. It oc- 

 curred to me that if one could lay down all the alta seams followed in 

 the explorations the result would closely resemble a contour map of the 

 fissures. Mr Reade, with the assistance of other officers, has compiled all 

 the information available regarding the occurrence of altas in the northern 

 part of the mine, and they are shown on the same scale as tlie mine map on 

 Atlas Sheet XIII. The result, however, requires some discussion because 

 of the irreguhirity of the lines and the distance which sometimes intervenes 

 between the two ore channels. At the northwest the fissures come nearly 

 together, and on the 1,930, the 1,8.50, and the 1,735 foot levels it is plain 

 from the position of the altas that there are at least two nearly parallel 

 fissures. On the 1,650 the alta forks, probably indicating the existence of 

 two fissures connected by a diagonal cross-course, for on the 1,5-10 and 

 again at the 1,440 tliere are two altas nearly parallel and at a considerable 



M0?J XIII -I 



