150 CHARLES R. KEYES 



amply demonstrated by isolated deposits which still remain in 

 protected localities, accidentally preserved through dropped fault- 

 blocks. For example, near Socorro there have been recently dis- 

 covered several such remnants of coal-bearing shales, both in the 

 Sierra Ladrones and to the east of the town. The deposits of the 

 latter rest in marked unconformity upon the rocks beneath, and 

 appear to have unconformable relationships with the strata above. 

 Although only about 100 feet of these shales now remain in the 

 locality mentioned, the recognition of their presence, their char- 

 acter, and their location is very likely to lead soon to discoveries 

 of very much greater developments. For this reason, and on account 

 of the important period which the deposits manifestly represent, 

 they have been called the Ladronesian series. 



The principal or great planes of unconformity which have been 

 made out are five in number. They all represent great erosion 

 intervals. The only similar phenomenon in the Mississippi 

 valley at all comparable to any one of them is the unconformity 

 at the base of the DesMoines series, in Iowa, Illinois, and Mis- 

 souri ; and it is now known that during this interval the entire Arkan- 

 san series of shales, over 10,000 feet in thickness, was laid down. 

 With two exceptions, all of the six series recognized are separated 

 by great unconformities, and there are also unconformities at the 

 base and at the top of the Carboniferous sequence. Besides these 

 five unconformities of wide extent, there are a number of local phe- 

 nomena of similar character, the exact magnitude of which is as 

 yet not fully determined. 



The character and location of some of these unconformity hori- 

 zons in the New Mexican field suggest their presence in the Kansas, 

 Oklahoma, and Texas sections where they have not before been 

 suspected. And this accounts for some hitherto inexplicable obser- 

 vations that have been made in those stat.es. 



Organic remains of the entire Carboniferous section are, with 

 few exceptions, strictly marine types. They are abundant through- 

 out the whole sequence, except perhaps at the very top. In most 

 localities where the rocks are well exposed fossils are as plentiful 

 as they are in the more familiar sections of eastern Kansas. Some 

 of the faunas are totally unlike anything described from other parts 



