Laws of Ncii.1 Mexico Mountain Ranges. — Herrick. 307 
paper, probably enough has been said to permit a comparison 
witli the other types of mountains named. 
The Caballos liave been referred to as co-orcHnate with the 
Sandias and Magdalenas. Both the San Andres and the Cab- 
allos were described incidentally in the American Geologist 
for November, 1898, in connection with a few remarks on the 
occurrence of copper and lead in New Mexico. The figure on 
page 289 will serve to show that the Caballos are of a much 
simpler type. In the section there given, while there is evi- 
dence of very profound metamorphism in the granites and low- 
er stratified layers, still one might say that this is an illustration 
of a tolerably pure block mountain. In our classification it 
would be neptunic-metamorphic, warping (or plastic) erosive. 
Indeed the erosive element does not greatly obscure what must 
have been the original facies. Everything, from the Subcar- 
boniferous to the Cretaceous, is involved and the series of "dis- 
tributive" faults extends several miles further east. This 
might be taken to represent the type given by Johnson in his 
diagram No. 3, even to the dropped block "a," though the case 
is not quite so simple as is represented. In these cases it is 
hardly proper to speak of the uplift ; in most cases it is demon- 
strably a depression on the down side which is responsible for 
the faulting. 
Passing to the Ladrones, which are also included by the 
critic in the category of block mountains, we have an entirely 
different type. Here is undoubtedly a metamorphic uplift. The 
vast isolated granite peaks of the central mass are like none 
of their neighbors. The Carboniferous limestone on the flanks 
does not break into the block faults described in the other cases, 
at least the faulting is insignificant and the strata arch gently for 
miles to a horizontal position. The limestone is the same as 
that of the Limitars ana Socorro mountain and contains Pro- 
dnctiis nchrascensis, Athyris argentea, Spirifer camerata and 
the familiar association, but the itratigraphical relations are 
very different. The range is metamorphic-neptunic, plastic- 
erosive. 
One further distinction may be in place here. The differ- 
ence in behavior of stratified participants in a complex moun- 
tain can be predicted, in general, from the nature of the asso- 
ciation. If the intrusive be a true igneous intrusive, the strat- 
