378 GEOLOGY OF THE COMSTOCK LODE. 



A discussion of the logarithmic equation as an expression of faulting 

 action leads to some very interesting results, some of which are as follows: 



Where a fault of the class under discussion has occurred, and where 

 the resulting surface has not been obscured by deep erosion, the original 

 surface can be reconstructed or calculated, and the amount of dislocation 

 determined. This is also true where more than one rock is involved. 



Where, as is nearl}^ always the case, the movement on the fault-plane 

 is equivalent to a inse of the foot wall, the hanging wall seen in cross-sec- 

 tion will assume the form of a sharp wedge, and this wedge will be ver}' 

 likely to yield to the compressive strain, and break across. 



If the movement of the foot wall on the fault-fissure were downward, 

 a. surface line would form which is scarcely ever met with in nature, and 

 the inference is that faults of this kind are of extreme rarity. This not 

 onl)' confirms the observations made in mines, but places the fact on a wider 

 basis of observation. 



If a fault, accompanied by compressive strain, takes place on a fissure 

 in otherwise solid rock, the walls are likely either to be distorted, if they 

 are composed of flexible material, or to be fissured into parallel plates if the 

 material is rigid. In the latter case the sheets of rock will also arrange 

 themselves on logaiithmic curves. 



If the intersection of a fault- fissui'e with the earth's surface is not a 

 straight line, but is sinuous or broken, the secondary fissures will be parallel 

 to the original one, and in the resulting surface each inflection of the trace 

 of the fissure on the original surface concave toward the lower country will 

 be represented on the faulted surface by a ravine, and each inflection con- 

 vex towards the lower countr}^ will result on the faulted surface in a ridge. 

 There is also a direct relation between the contours of the foot wall of such 

 a fissure and the surface contours. If the original surface was a horizontal 

 plane, the surface contours will be identical with the foot wall contours. 



Application to the comstock. — Tlio tlicory, thougli workcd out independently of 

 the Comstock, applies to it with much pi-ecision. Equations can be given 

 representing very closely the surface line of a cross-section, the amount of 

 the fault can be determined, etc. It can be shown that the erosion since the 

 beginning of the fault is very slight, that the canons of the range were pro- 



