GEOLOGICAL SETTING OF NEW MEXICO 239 



it constitutes the longest and best sedimentative record of which 

 we know. 



Huge as is the sedimentative prospect, erosive depletion looms 

 up in even vaster proportions. Thirty major unconformities 

 stand for a very much longer interval of time than that which 

 deposition occupied. Nowhere else on the face of the earth does 

 it seem that the stratigraphic record is so clearly defined for a 

 perfectly independent classification of geologic terranes according 

 to diastrophic movement. It is the one place of all where orotaxial 

 principles should sustain themselves under severest test. Any 

 world-scheme of formational arrangement must stand or fall when 

 fitted to this titan among rock sections. 



That the pre-Cambrian rocks beyond the southern Rocky 

 Mountains have never received the attention which they really 

 merit recent disclosures amply attest. It seems possible that some 

 day ere long they will divulge as clear a succession as did the transi- 

 tion rocks to EngHsh geologists a century ago. At least this is 

 certainly the most promising field for new and large results that 

 the American continent today offers in stratigraphy. 



Three grand successions are presented. There is first at the 

 top a thick section composed of relatively slightly metamorphosed 

 and mildly deformed rock masses; then, in the middle, separated 

 above and below, by a great erosional unconformity, a sequence of 

 terranes highly altered, closely flexed, and repeatedly broken 

 through by eruptives of various types; and third, at the bottom, 

 an intensely metamorphosed and sheared complex in which no 

 signs of classic origin are discernible. These grand successions are 

 respectively Proterozic, Archeozoic, and Azoic. 



To the Azoic basement are referred all of those lowest pre- 

 Cambrian masses which, intensely altered and profoundly deformed, 

 present no evidence of sedimentary origin. If any such classic 

 character ever existed all trace is now completely obliterated. 

 This intensely metamorphosed complex lying at the very bottom 

 of the exposed rock column is a new find. Its discovery is yet too 

 recent to enable its full significance to be properly evaluated. 



Composing this fundamental complex are mainly thinly foUated 

 gneisses, micaceous schists, squeezed granites, and other sheared 



