244 CHARLES KEYES 



limestone, which extends over the entire area of the state, reaches 

 far into Texas on the one hand, and on the other hand completely 

 over the Colorado dome to the Grand Canyon, where it 

 appears as the Aubrey limestone, has in New Mexico a thickness 

 of 5,000 feet. 



These unbroken limestones are the open-sea analogues of the 

 coastal coal measures of the Mississippi Valley. Where in Iowa 

 they are mainly represented by a great erosional interval, and in 

 Arkansas by 20,000 feet of shore deposits, in the New Mexican 

 field coal-bearing measures are all but completely vanquished. 

 Something of the enormous Arkansan series seems to find expres- 

 sion in the diminutive Ladronesian series with its bare 200 feet of 

 Alamito shales and a scant foot of coal. The last-mentioned for- 

 mation, which no doubt was once one of very considerable magni- 

 tude, is almost effaced through erosion which took place before 

 the laying down of the limestones, which in marked unconformity 

 rest directly upon these shales. 



Pennsylvanian, or upper Carboniferous, limestones attain a 

 thickness of 2,000 feet in northern New Mexico. There they 

 recline directly upon the surface of the old pre-Cambrian basement, 

 all else of the Paleozoics being absent. In the South, where they 

 reach a measurement of upward of 5 ,000 feet and are known as the 

 Hueco succession of limestones, they repose successively upon 

 Mississippian, Devonian, Silurian, Ordovician, and Cambrian 

 formations. 



In the North the great Hmestone plate is best known in the 

 lofty Sandia and Manzano ranges, east of Albuquerque. Through- 

 out this district it appears to be broadly separable into two strongly 

 contrasted formations— a lower shaly and black limestone, and an 

 upper member comprising chiefly massive blue and gray limestones. 

 To the inferior member, 1,000 feet thick, the title "Lunasian 

 series" is given. To the upper sequence, also about 1,000 feet in 

 thickness, the term "Maderan series" seems most appropriate. 



On the basis of the determined faunal characteristics the 

 stratigraphical position of the Lunasian series appears to corre- 

 spond nearly with that of the Missourian series of the Mississippi 

 Valley. Upon the same grounds the Maderan series is paralleled 



