Geology of 31 in h}g Camp in New Mexico. — Herrick. 259 
between the higher and hnver portions of the same series is in 
conformity with what has already been said as to the proba- 
ble method of concentration. Here at the summit there is 
less opportunity for percolation and none for deposition of 
solutions from other regions. The leaching, if it has occurred, 
has only impoverished the strata. 
In general, it may be said that any one of a number of im- 
pervious strata (quartzite or silicious shale) associated with 
the several limestone belts may become barriers to the trans- 
verse motion of the mineral-bearing waters and, by conse- 
quence, give rise to a metalliferous horizon. The ore in such 
cases is usuall}' concentrated along lines of least resistance, 
inclining at various angles within such horizons. These water 
courses produced "pipes" or "shoots" in the ore zone where 
great masses of lead carbonate, smithsonite and other miner- 
als were deposited obviously froin aqueous solution. 
The lead, however, must have originally been galena, as 
cores of that mineral are very generally found within masses 
of lead carbonate. The larger cavities or chambers are fre- 
quently exceedingly beautiful, and a single such chamber has 
frequently yielded a good fortune. The walls are water-worn, 
encrusted or stalactitic. Oracalcite, smithsonite and blende 
occur with the prevailing cerussite. 
Were the conditions as simple as hitherto implied the work 
of prospecting would be of the easiest, but, on the contrary, 
the whole area is intersected b}^ faults in two or more parallel 
series. One series of strike faults give rise to minor ridges 
parallel to the main axis on its western slope, repeating the 
sequence to a greater or less extent in each case till the level 
of the valley at the foot of the isolated Mt. Magdalena about 
three miles west of the main range is reached. The western 
margin of this faulted area is formed by an independent basic 
uplift, wiiich may be said to have prevented the sheet from 
reaching the degree of dei)ression to be expected theoretieall}'. 
This intrusive may be traced to the most northern crater of 
the series and is approximately parallel to the main axis. The 
strike faults above mentioned are quite numerous — from six 
to twelve major ones and manj'^ minor ones can be recognized. 
They are not strictly parallel to the range, but extend south 
80° east at right angles to the dip. The dip of the western 
