KXDLicn.] SOUTHERN AREA— POST-CRETACEOUS. 125 



Sweetwater Ilills. Tor a considerable distance north no dip is noticeable 

 except that to the west. jSrear the hills, however, we notice a slight inclina- 

 tion to the southward. It is not more than 2° or 3°, and unless a large area 

 is in view cannot be seen. From there the I^aramie beds continue iji a 

 westerly direction until hidden by Tertiary beds. From the stratigraph- 

 ical structiu'e of the entire region we see that this group forms a basin, 

 and, so far as we could determine, the yoiuiger strata are conformable 

 tliereto. This is the one that, in its surface appearance, has been desig- 

 nated as the Shoshone Basin. As we cross the strike of the Laramie 

 beds, wo notice that their dip decreases, amounting finally to only 

 about 2°. Lopse drift covers the blutis and valleys very extensively, 

 somewhat interfering with the recognition of continuations of strata. 

 From the facts which we obtained wath reference to the Laramie Group 

 of this region we may regard it as composed entirely of sandstones, 

 shales, marls, clays, and coals. 



Near the base heavy sandstones set in, soon superseded, however, by 

 shales. These contain strata of sandstones at varying intervals. A 

 number of coal-beds were found overlying these sandstones. The coal 

 is generally covered by a comparatively thin stratum of sandstone, upon 

 which follow clays, shales, and arenaceous marls. Higher up we find a 

 succession of sandstones interstratified with shale. Gypsum in the form 

 of selenite is quite trequently found in the latter. The higher members 

 of the group are composed of yellow and white sandstones, containing 

 several beds of coal, and dark, often carbonaceous shales. Sandstones 

 mediate the transition into the Lower Tertiary Groujjs. We may regard 

 the lowest coal-horizon as the most ijrodnctive one. In Colorado we find 

 the same character exhibited as to the utility of the coal. The total 

 thickness of this group, west of Eawdings Springs and irom there north- 

 ward, may be estimated at nearly 1,G00 feet. 



In the vicinity of Eawlings some coal is mined in the lower beds. The 

 demand does not warrant the i)rosecution of work during the entire year, 

 but a sufliciently large quantity can be disposed of to make the produc- 

 tion of coal remunerative. Near Fillmore and Summit we found a num- 

 ber of abandoned openings on coal-banks, some of which appeared to 

 extend into the veins for considerable distances. In most cases the roofs 

 wei'e either too unsafe, or the holes were fidl of water, so that we could 

 not make any extended examinations. East of Fillmore we found an old 

 tunnel, at the mouth of which a huge dump of slaked coal indicated 

 that a good deal of work had been expended on the vein. A section 

 obtained there of the strata immediately above the coal-bank may fur- 

 nisli a general idea of the beds usually associated with the coal. Begin- 

 ning with the top of the smaU bluff into which the tunnel was driven we 

 found : 



A-. YclloAv, middle-grained sandstones. Contain argillaceous bands 5 feet. 



i. Gray, laminated shales, exfoliating npon weathering 9 feet. 



/(. Yellow sandstone, with reddish stains. Fossil plants 2 feet. 



g. AVliitc, coarse-grained, argillaceous sandstone, with thin seams of light- 



yollow shales 7 feet. 



f. Y('llow sandsiones, ferruginous and hard, with Calamiten and other plants.. 3 feet. 



e. Light-gray very tine-graiued shales with minute crystals of selenite 5 feet. 



d. White coarse-grained sandstone, readily weathering into rounded forms 6 feet. 



c. Gray and drab, higlilj^ argillaceous shales and clays, with leaves and selenite. 4 feet. 



h. Carbonaceous shales, containing thin seams of coal 6 feet. 



a. Coal 8 feet. 



In connection with these outcrops of coal we had occasion to observe 

 the extensive alteration of exterior appearance produced by their taking 

 fire. At a number of localities we had observed brilliant red shales vnth- 



