392 GEOLOGY OF THE COM STOCK LODE. 



squares, and also, for comparison with them, the observations of Mr. J. A. 

 PhilHps at the Rose Bridge CoUiery. 



Chapter VII. contains the details for these localities and for the famous 

 deep boring at Sperenberg, near Berlin. Here it is sufficient to state that 

 on the CoMSTOCK the temperature of the rock rises about 3° F. for every 

 additional depth of 100 feet, or about twice as fast as in ordinary localities; 

 and that boiling water will probably reach the workings at some point not 

 long after the 4,000-foot level is passed. 



Observations have also been made in the Sufro Tunnel, and these when 

 plotted give a very remarkable result, for the curve shows that the tempera- 

 ture rises in a geometric ratio as the Lode is approached. This is capable 

 of no other explanation than that the east country is heated from a plane 

 in the immediate neighborhood of the Lode. Combined with the results 

 obtained from the shafts this curve, without any reference to geological 

 reasoning, indicates that the source of heat is at a vast depth compared 

 with that of the mines, and that the heat is communicated upward along or 

 near the fissure, and thence to the country rock by conduction. 



THE LODE. 



General character of the vein. The COuditioil of the LoDE dunUg tllC peHod 



in which the field work for this report was done was not what could have been 

 wished, for almost the only ore in sight was the remnants of the great bonanza 

 of the Consolidated Virginia and the California, and the accessible exposures 

 of the vein were meager and unsatisfactory. The study of the Comstock 

 was thus necessarily directed to the conditions of its occurrence rather than 

 to details of vein structure. 



A glance at the surface map shows that the Lode is along and wide belt 

 of vein-matter ramifying at each end into divergent branches,^ and the cross- 

 section exhibits a remarkably regular foot wall dipping to the east at an 



' The scale of the surface map is not large euougb to permit all of the minor fluctuations of thi' 

 walls to be shown, nor are the mine maps sufficiently complete to furnish data for a full exhibition of 

 these irregularities on a larger scale. For more detail the reader is referred to Mr. King's section on the 

 331-lbot level of tho Virginia mines. 



