148 CHARLES R. KEYES 



actually so enormous as it is, and as the recent measurements clearly 

 show, was never thought of. This maximum thickness is now 

 known to exceed 6,000 feet. Six great and important series have 

 been differentiated. As now recognized, they are, with their respec- 

 tive thicknesses, as follows: 



Unconformity 

 Cimarronian sandstones and shales 1,000 feet 



Unconformity 



Guadaloupan limestones 2,500 " 



Maderan limestones 700 " 



Manzanan limestones 1)3°° " 



Unconformity 

 Ladronesian shales and sandstones 100 " 



Unconformity 

 Socorran limestones 500 " 



Unconformity 



Of these, one series is Early Carboniferous, and is found only 

 south of the central portion of the state; two are of Mid- 

 Carboniferous age; and three belong to the Late Carboniferous. 



With the schematic, or standard, section of the American Car- 

 boniferous series, as represented in the Continental Interior prov- 

 ince, in Missouri and Kansas (II), may be paralleled the section 

 of the Southwestern province represented by New Mexico (I), and 

 also the eastern section of Pennsylvania (III), as usually given. 



Comparing in a general way the New Mexican succession of the 

 Carboniferous formations with that ^of the Upper Mississippi val- 

 ley, there is at once noticeable in the first-mentioned section a rela- 



