EASTERN FOOT-HILLS. 37 



Sulphate of lime •- 78.11 



Water 21.21 



99.32 



No organic remains have yet been found in the Triassic focmations 

 east of the Colorado Range. 



JuEASSic FOEMATioN. — Intimately connected with the Red Beds occurs a 

 series of loose friable sandstones, limestones, marls, and impure clays, pre- 

 senting great variety in color and texture, and passing from one to the other 

 by almost imperceptible grades. The entire series is usually composed of 

 fine-grained material, and the clays and marls show a more or less laminated 

 structure. These beds have been referred to the Jurassic age. 



While the prevailing character of the Triassic beds is a deep red sand- 

 stone, the overlying Jurassic rocks possess a slightly reddish tinge, but are 

 marked by beds of orange, purple, and lavender-colored strata, which con- 

 sist largely of argillaceous material. Narrow beds of limestone occur in 

 both formations, while gypsum, which forms so prominent a feature in the 

 Triassic, is found in thin, narrow seams, in what vfould appear to be several 

 different horizons in the Jurassic. 



The line which has been adopted as forming the boundary between 

 the Triassic and Jurassic periods is a somewhat arbitrary one, not being 

 based upon any broad structural or palseontological evidence, or, indeed, 

 upon any clearly-defined lithological distinction. Where the upper forma- 

 tions of the Triassic period consist of the deep red compact sandstones, 

 and the overlying strata are friable light-colored beds, the line of separation 

 has been taken at the summit of the more massive red series. In many 

 places, however, the top of the. Red Beds possesses a yellowish shaly char- 

 acter, shading into the upper series, rendering a sharp line of separation 

 somewhat difficult to establish. As the upper . beds, however, are much 

 more easily decomposable, they have suffered considerably from erosion, 

 and have been worn out into longitudinal depressions, or valleys, between 

 harder layers of rock, forming a somewhat marked physical feature of the 

 ridges, and at least offering a convenient division between the two series of 

 rocks. No organic remains sufficiently well preserved for specific deter- 



