538 FLORA OF THE LARAMIE GROUP. 



uie to conclude that during the ni)he:ival of the Front Eange a break 

 must have occurred along a line near the western base of Table Mount- 

 ain, forming a crevice through which issued the matter that forms the 

 basaltic cap of these hills. The eastern edge of a broad strip of land 

 lying to the west of this break dropped down until the entire strip of 

 land assumed a vertical position or was tilted somewhat beyond the 

 perpendicular. This brought the Laramie on the east side of the Creta- 

 ceous with its upper strata at the extreme eastern, while the coal seam 

 at its base occupied the extreme western side of the displaced rock. 

 The degree of inversion varies slightly at different points and may 

 have been much greater in some places. This will probably account 

 for the discovery at one time of a certain Cretaceous shell (Mactra) above 

 a vein of coal in a shaft about 4 miles north of Golden, and about which 

 considerable has been said in discussing the age of the Laramie gi'oup. 

 I visited the spot, but found the strata so covered by wash that I was 

 unable to determine their nature. 



The collections made at the base of South Table Mountain in a dark 

 and very soft, tine-grained, siliceous-ferruginous sandstone, commonly 

 called tufa, were both more abundant and better preserved than those 

 from the valley, and in them have been found several rare and interest- 

 ing forms. Ficus irregularis was one of the most common, and Berche- 

 mia multiiwrvis was found. Palms abounded, but only as fragments of 

 narrow portions of leaves. On the surface oi the ground, quite well 

 down toward the bottom of the valley, were found numerous fragments 

 of palm wood in the silicified state, as chert, very hard and admitting 

 a high polish. The leaf scars are clearly exhibited, and the vascular bun- 

 dles and ducts are beautifully shown in cross and longitudinal sections. 



At the locality known as Girardot's coal mine, some 5 miles east of 

 Greeley, Colorado, on the open plains, Laramie strata were found con- 

 taining characteristic mollusks in great abundance, but no plants ex- 

 cept the wide-spread Ilalymenitcs major, which occurred in profusion 

 immediately over the shell beds. Large branching forms were found, 

 as well as forms variously curved and crooked. They seem to be to 

 some extent concretionary, and are composed of iron oxide and sand 

 with a little calcite. 



At the mouth of the Saint Vrain, near Platteville, where aday was 

 spent, these forms occurred again in equal abundance and variety. Two 

 species were found here, and ])erhaps three. Specimens of petrified wood 

 from a large stump, probably coniferous, were collected, but no traces 

 of any other form of plant life were detected. At this point we seem 

 again to have the very base of the Laramie overlying a bluish Creta- 

 ceous clay. 



The collections from Carbon Station, Wyo., are much more satisfactory 

 than those from the Colorado beds. The station and adjacent track of 

 the Union Pacific Railroad at this point are located in a monocliual val- 

 ley running north and south, or at right angles to the railroad. A fault 



