SUMMARY. 395 



but represent sheets of rock triturated and decomposed without any great 

 translocation of material. I'liis fact is determined chemically, but confirmed 

 by the relation of the clays to the faulted structure; for while the}- are excess- 

 ively abundant in and near the secondary fissure where the influence of the 

 surface interfered with the develojjment of the regular system of fissm-es 

 found in the lower levels, they are comparatively i-are and thin below the 

 bottom of the great horse. 



Infrequency of lenticular openings. TllC SCCtioUS sllOW that the lower pOrtioUS 



of the Lode, considering its enormous scale, are narrow and remarkable 

 for the absence of the lenticular openings which frequently characterize 

 faulted veins. If the hypothesis developed under the head of the structural 

 results of faulting is correct, this peculiarity is almost a necessary conse- 

 quence of the conditions under which the Comstock formed, for the slip of 

 the actual walls of the vein is on that theory only the relative movement of 

 two successive sheets, and if these are assumed to be twenty -five feet thick, 

 it would not amount to above a hundred feet. The intensity of the fault- 

 ing action was less toward the ends of the Lode than near the middle, 

 the force being distributed over a wide area by the branching, and probably 

 also to some extent by numerous east-and-west fractures, singly of small 

 extent. The south end of the main Lode seems to have been less forcibly 

 faulted than the north end This is partly ascribable to the character of the 

 foot wall, stratified rocks being less rigid than massive ones, and partly to 

 the fact that the dip is about 10° less 



Character of the spaces occupied by bonanzas. TllC CvideUCC appCarS COnclusivC that 



the ore bodies occupy spaces which once inclosed onh* fragments of country 

 rock, with numerous interstices. These openings seem to have been due to 

 faulting action variously modified by local circumstances In the Consoli- 

 dated Virginia and neighboring mines a projecting mass upon the foot wall 

 gave rise to a local rent in the diabase. In the Virginia group an irregu- 

 larity in the dip of the foot wall prevented the broken edge of east country, 

 the great horse, from following the main body to its final position; and a 

 crescent-shaped opening resulted which furnished an opportunit}- for the 

 deposition of an extensive system of bonanzas. In Gold Hill, on the other 



