CARBONIFEROUS FORMATIONS OF NEW MEXICO 



CHARLES R. KEYES 



Several features contribute to make the Carboniferous section 

 of New Mexico the most noteworthy of the American continent. 

 Its enormous thickness, the strictly marine nature of its sediments 

 which constitute it the most imposing limestone plate among the 

 known formations of the country, the feeble development of exten- 

 sive shale beds so familiar elsewhere, the total absence of workable 

 coal-beds which are the one feature of all others that is usually 

 characteristic wherever the rocks of this age are found, the existence 

 of a number of great planes of unconformity clearly indicating 

 enormous erosion intervals, and the great abundance of organic 

 remains, are some of the more salient points contrasting the Carbon- 

 iferous of New Mexico with the sections of the same system elsewhere. 



It has been unfortunate that the notes which have been made 

 during the past half- century upon the Carboniferous rocks of the 

 southwestern United States have been so meager, and so disconnected, 

 and the publications in which they have appeared so widely scat- 

 tered. From the literature alone, practically no correlation of sepa- 

 rated sections has been possible. Confronted with these excep- 

 tional conditions, it . soon became one of the main objects in the 

 course of the geological survey of the New Mexican region to examine 

 not only all of the Carboniferous exposures, as far as possible, and 

 to correlate them in the field, but from the point of vantage thus 

 gained to connect with these broader observations the fragmentary 

 notes previously published. 



The great thickness of the "Upper Carboniferous hmestones" 

 of the southern Rocky Mountain region has always been a matter 

 of comment among all those who have traversed this part of the 

 country. Few of these persons have ventured to put the measure- 

 ment of these great limestones above about 2,000 feet. That the 

 connected section of the Carboniferous strata as represented within 

 the boundaries of New Mexico, indicated a thickness which was 



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