8o 



CHARLES KEYES 



Mountains region all strata down to the pre-Cambrian complex 

 are removed and the Pennsylvanian limestones rest directly upon 

 the ancient crystallines, in southern New Mexico the same limestone 

 plate reposes on the beveled edges of all of the older and somewhat 

 deformed Paleozoics (Fig. 2). 



Certain peculiarities in the areal distribution of the Paleozoic 

 formations in southern and central New Mexico at once raise far- 

 reaching questions in diastrophics. Among them not the least 

 significant is whether the northern limits of the several major ter- 

 ranes are approximately the original boundaries of deposition, or 



Fig. 2. — Relations of periodic formations south of Rocky Mountains 



whether these periodic terranes once extended indefinitely northward 

 over the tract which later was upraised into the Rocky Mountain 

 arch. 



Casual consideration of present conditions points sometimes to 

 one conclusion and sometimes to the other. Critical evidence 

 centers on the character of the marked unconformity at the base 

 of the Pennsylvanian section. The present northern boundaries 

 of the other periodic terranes are very close together (Fig. i). The 

 strata are all virtually Hmestones. There are practically no 

 characteristic shore deposits represented. Positions of none of the 

 formations indicate that there are any well-defined overlaps. All 

 features considered, the conclusion appears inevitable that the 

 strand oscillations at different times were of great magnitude, 



