338 GEOLOGICAL SURVEY OF THE TEKEITORIES. 



Feet. 



1. Argillaceous sbale, with ferruginous concretions 96 



2. Shaly sandstone, sometimes in banks and very bard, with fossil dicotyledo- 



nous leaves 11 



3. Alternating beds of shale and shaly sandstone 106 



4. Sandstone in bank 11 



5. Sbale and clay banks, mostly clay-covered 145 



6. Bituminous clay 10 



7. Conglomerate, lower bank 27 



8. Fine-grained sandstone, with thin layers of coarse-grained sandstone 32 



9. Conglomerate, topi^ed with coarse sandstone 37 



10. Hard, yellow, liue-grained micaceous sandstone 32 



11. Conglomerate to top ' 40 



547 



la these 547 feet of measures above the coal, the upper part, mostly 

 conglomerate strata alternating with sandstone, is 168 feet. Comparing 

 this section to that of Colorado Springs, above the Gehrung coal, 

 where the same kind of conglomerate tops the Lignitic formation, we 

 cannot but find a remarkable analogy, not to say identity, between 

 both. At Colorado the conglomerate, as should be expected from 

 the greater distance to the point where the materials have originated, 

 is comi)Osed of smaller pebbles. The thickness of the same measures is, 

 too, reduced by erosion. But the relation and alteruance of the strata 

 is similar. The same can be said of the Upper Lignitic of Cahon City 

 and of other localities reported by Dr. Ilayden. From this, and also from 

 the conform ability of these conglomerate beds with those of the Lignitic 

 which they overlie, I am disposed to consider them as of the same age 

 and as marking the close of the Lignitic group. The con form ability of 

 the strata is especially remarkable at Evanston, and easily recognized 

 along the hillsfacing the river, cut nearly vertically and sloping northeast 

 by a dip of about 10°. If, as it has been supposed, this conglomerate forma- 

 tion was more recent and had covered Tertiary strata of different 

 groups, this alternanco of conglomerate with sandstone strata, in per- 

 fect concordance to the soft bituminous clay-beds which they overlie, is 

 unexplainable. Further evidence, however, will be afforded on this 

 important question. The amount of materials brought up for this forma- 

 tion is beyond computation. They not only form the essential com- 

 pounds of hills over wide areas, but their debris covers the i)lains for 

 hundreds of miles around the nuclei which now stand as mere dwindled 

 monuments of a wide-spread, as yet inexplicable agency. The pebbles 

 composing the conglomerate of Evanston vary in size from that of a 

 pea to that of the head : the most common are as large as tbe fist. 

 They are all rounded, without exception true pebbles, as if they had 

 been rolled by water for a long time. As at the other places where they 

 have been remarked, they are of the same materials as those which 

 now compose tbe mountain-ridges of the vicinity, and are glued together 

 by a kind of calcareous cement, hardened locally by ferruginous infiltra- 

 tions. 



Dicotyledonous fossil-plants are found in quantity in a bituminous 

 shale overlying the u[)per coal of Evanston, and, too, in the sand- 

 stones marked on the sections Nos. 2, 3, 4. This sandstone is hard and 

 compact enough at some places to afford good building-materials. On 

 one of the blocks used for construction at the mines I saw a well-pre- 

 served leaf of a Fopuhis, larger than any as yet found of this genus, in 

 a fossil state. It measured more than C inches in length without the 

 petiole. In the shale above the coal, the leaves are crowded, heaped upon 



