100 
ISOSTATIC THEORY 
especial geologic description, about 1880, no such thing as a 
distinctive desert geology was entertained. Possibility of a definite 
geographic cycle in land sculpture was one of the modern earth 
concepts yet undreamed. Competency of the wind as a general 
erosive agency was not yet established. Operation of epeirogenic 
movements was just beginning to be distinguished and was yet 
but little understood. Omission of such basic considerations, as 
we now know them to be, necessarily led to curious aberration in 
interpretation of the phenomena presented by lands of little rain. 
When I first took up residence on the arid Mexican tableland 
it was with special reference to being near the enticing novelties 
of desert tectonics and the possibilities of its practical relations 
as an aid to mining. Before entering the field I already had 
many grave doubts concerning the alleged genesis of its make-up. 
I particularly desired to lay hands, as it were, on the reputed 
fault-lines of the mountain blocks. I wanted to find some tectonic 
relationship of that impossible freak — the laccolith. I wished to 
discover some measure of the competency of the wind under the 
stimulus of aridity as a graving tool in arid land sculpture. 
At first glance the fault-block structure of the desert ranges 
seemed all too simple — as simple, perhaps, as it did to the 
imaginative author of the celebrated hypothesis. I fancied that 
I had only to go to the foot of a mountain ridge, determine off¬ 
hand the approximate location of the bounding rupture, and then 
find along the fault-scarp a line of miners’ cabins which would 
enable me to read the ore signs as from a printed page. But the 
mines were scattered over the mountain everywhere except along 
the piedmont scarp where Duttonian argument demanded. Not 
to be deterred by so unpropitious a beginning examination of the 
cross-chasms was instituted. The Tijeras Canyon, deep as the 
Royal Gorge, separating the lofty Sandia and Manzano sierras, 
g^e a section a mile in vertical exposure to the very roots of the 
mountains. Palomas Gap, likewise deep, between the Sierras de 
los Caballos and San Cristobal, gave similar magnificent 
prospects from top of mountain to bottom. Soledad Canyon, 
which bisects the Sierra de los Organos, presented also gorgous 
views. There were innumerable other determinative exposures. 
None of these numerous chasms, or cross canyons, which tra¬ 
versed the so-called fault-scarps showed that there had been any 
appreciable dislocation along the line which the scarp was supposed 
