GEOLOGICAL SETTING OF NEW MEXICO 237 



abundant and of many colors. If he could have viewed them 

 they would surely have gladdened the heart of Johannes Lehmann. 

 Had the grand old pioneer in the field chanced to dwell in this 

 country instead of Saxony the Erzgebirge might never have 

 become so famous; and Die Untersuchungen uher Entstekung der 

 altkrystallinischen S chief ergesteine might have had the desert range 

 of New Mexico for the central theme of his great epic. 



The massive plu tonic rocks, the granites, diorites, gabbros, 

 and diabases, cut and intrude the pre-Cambrian complex in all 

 directions. Their surface types appear to have utterly disappeared, 

 probably during the long periods of erosion as indicated by the 

 great unconformities. 



Volcanics belong to all ages from the Cretaceous onward. San 

 IVIateo is one of the majestic volcanic piles of the continent. It 

 now stands perched high upon a lofty Cretaceous pedestal. A 

 forest of volcanic necks stretches away to the northward. Modern 

 basalt flows cover hundreds of square miles. Older lava streams 

 constitute the resistant cap of many plateau plains. Intrusive 

 sheets run for scores of miles across the plains like great walls of 

 Cyclopean masonry. Laccolithes (Fig. 3) display their tectonic 

 origin rather than formation through simple hydrostatic welling. 

 Cinder cones are numerous (Fig. 4). Beside the fine cone of 

 Capulin that of famed Vesuvius sinks into utter insignificance. 

 The phenomena of classic Auvergne and the Phlegraean fields are 

 reproduced again and again but on grander scale. 



Stratigraphical succession in New Mexico is instructive to an 

 extraordinary degree. It is, perhaps, the most complete to be 

 found in any state in the Union. Curiously enough, above the 

 pre-Cambrian crystalline complex highly resistant rocks compose 

 the lower half of the geological column; while in strong contrast 

 weak friable beds are segregated in the upper half. With a close- 

 patterned orogeny this disposition has telling effect upon the final 

 relief expression. 



The geological column attains an enormous thickness. Arch- 

 eozoic, Proterozoic, Paleozoic, Mesozoic, and Cenozoic sections are 

 each about 10,000 feet in vertical measurement. Altogether there 

 are 50,000 feet of strata reposing upon the non-clastic Azoics. It is 



