ENDucn.] EAST OF WIND KIVER RANGE — MESOZOIC FORMATION. 87 



Prom this table it will be seen that the daily mean temperature affects 

 that of the water but slightly in the centre of the spring. Near the 

 shore so many different factors enter into consideration which may tend 

 to produce a variation of a few degTces, that the true index must be taken 

 from elsewhere. 



Eegarding the source of heat which supplies the warmth of the water, 

 I consider it due to chemical changes going on within the strata through 

 which the moisture finds its way. As hot water is a more effective solvent 

 than cold, the channels by which the spring obtains its supply will grad- 

 ually increase in size. From this it may be inferred, provided the chemi- 

 cal action continues in a proportionate ratio, that the waters of the spring 

 may still grow warmer m the course of time. 



A petroleum spring also occurs near Camp Brown, originating, prob- 

 ably, in the same rocks. We observe the globules of oil rising in water 

 and eventually accumulating near the banks. Here a somewhat exten- 

 sive deposit of hardened black oil is formed. It bums very readily, and 

 appears to be nearly pure. 



REVIEW OF THE IIESOZOIC aROUPS EAST OF THE WIND RIVER RANGE. 



All of the Mesozoic Groups in this region may be regarded as typical 

 to a certain extent. Several of them show a considerable amplification 

 to the eastward, but otherwise remain tolerably constant. In their rela- 

 tions to each other they are constant throughout. 



Fox Hills Group : 



Sandstones and arenaceous shales near base. Following are heavy beds of 

 shale. Indications of coal near bottom and top. Shales and ni)i)er sand- 

 stones are more or less micaceous. Thinly bedded sandstones with some 

 shales near top. Massive yellow sandstones close the group. Fossils : Inoce- 

 ramus and indistinct jilants. 



Thickness 500 feet. 



Colorado Group: 



Dark gi'ay shales, finely laminated. Slightly calcareous near base. Upon ex- 

 posure the shales turn light gray and white. In the ujiper half thin bank of 

 argillaceous limestones. Near the top the shales becomes lightly arenaceous. 

 Fossils: Inoce/ramus, Ostrea congesta. 



Thickness 600 feet. 



Dakota Group: 



Yellow and brown shales near base, containing thin strata of sandstones. 

 Some carbonaceous shales a little higher up. In the middle sandstones, sep- 

 arated by thin bands of dark shale. Massive yellow, white, and brown sand- 

 stones near top. Dark yellow and brown shales close the group. Fossils : 

 G-ryphcBa and indistinct remains of jilants. 



Thickness 400 feet. 



Jura : 



Dark calcareous shales, covered by heavy beds of dark blue limestone, are near 

 the base. Yellow shales and marls follow, with some thin iuterstrata of yel- 

 low or white sandstones. Some limestones above this. A series of yellow, 

 white, pink, and greenish marls and shales close the formation. Fossils: 

 Bclemtdtes, Gryphcea, lihi/nchonella, Lingula, Modiola, Pecten, and others. 



Thickness 200 to 220 feet. 



Trias : 



Some light red and white sandstones near base, separated by thin beds of red 

 or brown shales. ISIassive bright red shales, with dolomitic intcrstrata higher 

 up. Heavy beds of red sandstone follow. Above these a series of red, pink, 

 yellow, and white sandstones, some of the coarse-grained. Shales occur with 

 these latter sandstones and close the formation. A decided thickening of the 

 upper beds may be observed to the eastward. No fossils. 



Thickness 800 to 1,200 feet. 



Adding these figures, we obtain for the Mesozoic division of this region 

 a total thickness of 2,500 to 2,920 feet. 



