320 GEOLOGICAL SURVEY OF THE TERRITORIES. 



This last stratum is underlaid by the Cretaceous black shale No. 4. In 

 some places No. 27 is the last member of the section, and is, tlierefore, in 

 immediate superposition to the black shale. From No. 17 to 28, and 

 j)erhaj)s already from the upper member, which is covered, the whole 

 measures form a single group of white or yellowish ferruginous sand- 

 stone-beds, separated by bands of hard laminated clay, mostly sandy or 

 passing to sandstone, the whole measuring 178 feet. The characters of 

 this group, as clearly recognized here, are as follows: 



1st. Its general color is whitish gray, so white indeed, sometimes, 

 that the lower strata, seen from a distance, appear like banks of lime- 

 stone. 



2d. Though generally hard, it weathers by exfoliation under atmos- 

 pheric iuhuences, and its banks are thus molded in round undulations; 

 and, as it is locally hardened by ferruginous infiltrations, it is often too 

 concretionary or grooved in cavities, so diversitied in size and forms 

 that sometimes the face of the cliffs shows like the details of a compli- 

 cated ii rch i tec t u re. 



3d. It is entirely barren of remains of animals. 



4tb. On the contrary, from its lowest stratum to its upper part, it 

 abounds in well-preserved remains of marine plants or fucoids, which, 

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



ath. 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. 



The disposition of the strata and their compounds is about the same on 

 the otber side of the Purgatory Eiver, opposite Trinidad, where the 

 section is from top downward : 



Feet. 



1. Hard ferru<j;inons shaly sandstone with few remains of fncoids, but abun- 



dance of debris of laud-plants 25 



2. Hard whitish sandstone, full of fncoids 57 



o. Shaly sandstone, with same abundance of fncoids 50 



4. Soft laminated ferruginous sandy clay, with fncoids 11 



5. Ferruginous shale, with fncoids 4 



6. White block-sandstone, l)arren 5 



7. White sandstone, with fucoids ". 22 



8. Ferruginous shaly sandstone, with fucoids 33 



9. Black shale of No. 4, Cretaceous 147 



10. Covered space, sandstone and shale to bed of river 153 



In both these sections the remains of marine plants are remarked in 

 most of the sandstone-strata and their intermediate clay-beds, and as 

 abundant at the base as near the upper part. And in this last section 

 they are seen mixed with fragments of land-i)Iants, even to the top of the 

 sandstone cut like a tower at the point of the highest hiH facing Trini- 

 dad. 



In passing from the black shale of the Cretaceous No. 4 to this group 

 of sandstone-beds overlaying it, the difference in the characters is strik- 

 ing, not oidy in considering their com{)ounds, but in the class of fossil re- 

 mains which they contain, the traces of deep marine life predominating 

 in the black shale, while here they have totally disappeared. The 

 absence of the upper Cretaceous formation No. 5 might be taken into 

 account for explaining this difference. We will see elsewhere that it is 

 not the case, -and that the upi)er Cretaceous sandstone-beds are as 

 definitely cliaracteiized by their fossil remains as a deep marine forma- 

 tion as tlie second group No. 4. Now, in the sandstone above No. 4, 

 marine life still marks its activity only by the abundant remains 

 of fucoi<ls, indicating by their growth a comparatively shallow water. 

 I'hey point out, therefore, to a slow upheaval of the bottom of the 



