28 EXPLORING EXPEDITION FROM SANTA Ffi 



Section of strata at Middle Si>i-h/(/ of ('hiutrron. 



1. Coarse gravel from disintegrated conglomerate - (! 



2. Spongy, tufaceous limestone, cream-colored - 3 



3. Soft, chalky tufa, cream-colored 



4. Laminated, tufaceous limestone, cream-colored '. . . G 



5. Massive, tufaceous limestone, iipper part hardest, containing halls of red and 



black scoria 50 



6. Cream-colored tufa, similar to No. 5, but softer 19 



7. Hard, foliated tufaceous limestone 5 



8. Yellow or reddish, soft, massive sandstone 40 



The cream-colored tufaceous limestones of the above section are the equivalents 

 of the lower tufaceous limestone of the Arkansas, and, though containing no fossils, 

 are doubtless Tertiary. The balls of scoria which they include, though not positive 

 evidence of the fact, may be regarded as an indication that volcanic action was going 

 on somewhere in this vicinity during their deposition. If this was the case, the scoria 

 must have been derived from the vicinity of the Raton Mountains, where volcanic 

 eruptions were taking place, geologically speaking, about that time. 



Scoria is very frequently contained in the Tertiary strata near the Rocky Mount- 

 ains; a fact which has suggested the thought that the water from which these tufaceous 

 limestones were deposited may, in some instances, have been heated, and that this is 

 one reason why they contain so few fossils. 



The sandstone which forms the base of the section, at the Middle Spring of the 

 Cimarron, will be soon noticed, in connection with the group to which it belongs; but 

 its place in the series, as has been stated, is below the Lower Cretaceous sandstone. 



We have here abundant evidence of the entire unconformability of the Tertiary 

 beds with those on which they rest, and that they were deposited in basins scooped out 

 of the underlying rocks, doubtless by subaerial action, precisely as similar valleys or 

 basins are forming at the present day. 



A few miles further westward the Lower Cretaceous, and even some portions of 

 the Middle Cretaceous strata, are found in place, and there is no question but that they 

 once stretched over all the adjacent country, and occupied the place since held by the 

 Tertiary beds, but, by the long action of eroding agents, they had been entirely re- 

 moved or deeply excavated before the Tertiary limestones began to be deposited; and 

 that subsequently this latter series filled up and obliterated all traces of that ancient 

 denudation. During the present epoch the process of erosion has again begun, and the 

 valleys of the Cimarron and Arkansas are being for the second time excavated. 



GROSSING OF GIMARRON TO ENGIIANTED SPRING. 



JURASSIC ? ROCKS. 



At the crossing of the Cimarron, and for some miles west of that point, the Ter- 

 tiary strata have been entirely removed; the bottom of the basin exposed and deeply 

 eroded. It is here composed of a. series of strata of which the sandstone, King at the 

 base of the cliff at, the Middle Spring, forms a part. This series consists of a number 



