GEOLOGICAL PAPERS. 143 



the divide is capped with lava sheets. Still further south the granite 

 base rises into a mountain range, the Black range. Mountains on 

 either side of the divide rise to altitudes above the divide, but streams 

 have cut canyons through them or have passed around their extremi- 

 ties. Detached ranges not far from the Rio Grande rise to heights 

 of 8000 to nearly 11,000 thousand feet. The Ladrone, Magdalena 

 and Caballo are the principal. But there are three groups or clusters 

 of ranges prominent in situation, magnitude, general elevation and 

 mining importance, namely, the Sangre de Cristo, or Red mountains 

 (from the red feldspar of the granite ), in the north-central part, the 

 Black mountains in the southwest (from the black clothing of pine 

 forests), and the White mountains in the southeast. They form a 

 right-angled triangle, of which the hypotenuse is the line from the 

 Sangre de Cristo to the Black mountains. 



New Mexican orology well illustrates the principle that, in crust- 

 wrinkling, horizontal thrust is from all directions and not from one or 

 two, as in the action of a vise. However, the lines of weakness may 

 not run in all directions ; but it ajDpears that, in New Mexico, the 

 strata were too evenly laid to allow any great differential of resistance. 

 Perhaps the absence of those enormously thick and rigid barriers to 

 compression, the Cambrian, Silurian and Devonian rocks, may have 

 had an influence in directing a distribution of effects to various points 

 of the compass. 



Mountain evolution did not cease in New Mexico until late Tertiary, 

 if it has yet ceased. Extensive local faulting, totaling, in cases, 1000 

 feet or more, accompanied or followed elevation. This movement is 

 still probably progressing, as is indicated by frequent slight earth- 

 quakes, local in perceptible effects. About the center of the terri- 

 tory a good number of seismic agitations occurred the present year 

 (1904). Whether dislocation progresses by elevation of mountain 

 masses, and corresponding slipping of strata in contact about the 

 bases, or by extension of old faults further removed, is a question the 

 solution of which may come by observing if changes of position oc- 

 cur in mining tunnels intersecting faults. Some suppose the faults 

 increase without elevation, which is not probable unless a reason can 

 be given for cavernous conditions. From the traditions of the Pueblo 

 Indians and descendants of the early Spanish settlers, and from the 

 evidences of former successful agriculture and large population where 

 neither of these conditions exist to-day, the inference has been drawn 

 that there is a general subsidence of the plateaus, but such data do 

 not seem to warrant the conclusion. It is true that certain altitudes 

 are necessary to cause aqueous precipitation, but these altitudes are 

 not the same in all sections. Some high mountains secure very little ; 



