3Iesozoic and Cmnozoic Geology and Paloiontology. 99 



contains well preserved, large, characteristic shells iu ferruginous con- 

 cretions. But soon the plain appears cut by undulations which 

 already, one mile from Trinidad, have their tops strewn with large 

 broken flags of sandstone, over which no other trace of fossil remains, 

 but marine plants or fucoids are seen. A little farther from the town, 

 the same sandstone is in place, immediately and conformably over- 

 Ijang the black shale; and in entering the small valley of the Raton, 

 the road curves around steep hills, whose base rests upon the fucoidal 

 sandstone, and whose sides, exposed by denudation, are blackened by 

 outcrops of coal at different altitudes. A section, along a small branch, 

 in whose banks the lignite-beds appear in succession down to Raton 

 creek, and then down this creek to Purgatory river, where the Fort 

 Pierre Group is exposed, shows the lignitic 300|- feet, succeeded by 

 178 feet of sandstone. The characters of the sandstone are as follows: 



First. — Its general color is whitish-gray, so white indeed, some- 

 times, that the lower strata, seen from a distance, appear like banks 

 of limestone. 



Second. — Though generally hard, it weathers by exfoliation under 

 atmospheric influences, aud/lts banks are thus molded in round undu- 

 lations; and as it is locally hardened by ferruginous infiltrations, it is 

 often too concretionary or grooved in cavities, so diversified in size and 

 forms, that sometimes the face of the cliffs shows like the details of a 

 complicated architecture. 



Third. — It is entirely barren of remains of animals. 



Fourth. — From its lowest stratum to its upper part,, it abounds iu 

 well-preserved remains of marine plants or fucoids, which, at some 

 localities, are seen even in the sandstone over lignite-beds. 



Fifth. — In its upper part, the sandstone or the shales of this group 

 are mixed with broken debris of land-vegetation, with which also 

 fucoidal remains are found more and more abundant in descending. 



In passing from the black shale of the Fort Pierre Group to this 

 group of sandstone beds overlaying it, the difference in the characters 

 is striking, not only in considering their compounds, but in the class 

 of fossil remains which the}^ contain, the traces of deep marine animal- 

 life predominating in the black shale, while here they have totally dis- 

 appeared. In the sandstone, marine life still marks its activity onl}' 

 by the abundant remains of fucoids, indicating, by their growth, a com- 

 paratively shallow water. They point out, therefore, a slow upheaval of 

 the bottom of the sea in which they appear to have lived; for their stems 

 penetrate the sandstone in every direction. And this indication is 

 still more manifest in the great abundance of _ debris of land-plants, 



