562 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



The Hardgrave sandstone is red or gray in color. It varies from fine shaly sandstone to con- 

 glomerate and is almost wholly of a tuffaceous character. The most common color is red, rang- 

 ing from brick-red to duU brown, but much of it is gray, and the two colors are intermingled 

 irregularly in the samd bed. The bedding is generally well marked, but in a few localities the 

 massive outcrops show little trace of stratification. Where the sediments are fine the sandstone 

 passes into shale, which occasionally shows a decided slaty cleavage and breaks up into long, 

 slender, pencil-shaped fragments. Generally the sandstone is so fine as not to appear granular 

 and breaks with a splintery fracture. * * * When the coarser forms of Hardgrave sand- 

 stone are broken the fracture generally passes around the grains instead of through them, 

 allowing them to stand in relief upon the fracture surface and make it rough. Rarely it is 

 hard and flinty, much fractured, and veined. * * * Carbonate of lime is the principal 

 cement, but in the red and weathered forms oxide of iron plays an important part. * * * 

 Coarse gray sandstone and fine conglomerate are much less abundant than the finer forms. 

 * * * [The material] is mainly volcanic sand, made up of crystal fragments of plagioclase 

 feldspar with many lapilli, usually more or less vesicular, and often filled with minute lath- 

 shaped crystals of feldspar, which are for the most part so altered that their polysynthetic 

 twinning, if present, can not be seen. Many of the feldspar fragments are plagioclase, but a 

 somewhat smaller number appear to be orthoclase and possibly some quartz. One of the 

 striking features of this sandstone, apparent only on microscopic examination, is the paucity of 

 quarts. * * * The maximum thickness of Hardgrave sandstone as measured half a mile 

 north of Donnerwirth's may be 850 feet but is possibly much less. 



According to Hyatt ^**"' the Hardgrave sandstone contains many fossils having 

 affinities with the lowest or infra Lias, and some which might even have occurred in 

 the uppermost Triassic or Rhsetic. Hyatt further says : 



On the other hand, some forms have very close relations to the same genera as they appear 

 in the Mormon sandstone, or Oolite, of the same locality. Pinna, Gervillia, Ctenostreon, Ento- 

 lium, Trigonia, and Cidaris show an assemblage of upper Lias types. The species of Entolium 

 and Ctenostreon are closely related to those . of the oolite above, and one species of Trigonia 

 resembles the young of a species from the Oolite of western Europe. The most conclusive evi- 

 dence, however, is furnished by the single well-preserved specimen of Glyphea * * * and the 

 Goniomya, allied to G. v-scripta Agassiz. 



After giving a list of 28 species and discussing the significance of Glyphsea, 



Hyatt says : 



Such forms as these and the evidently close alliance and probable continuity of the fauna 

 through migration with that of the Mormon sandstone suggest that the Hardgrave sandstone 

 should be classed as upper Lias in spite of the large number of forms which are represented by 

 species occurring also in the lower and middle Lias in Europe. 



Diller continues the description of the Jurassic strata as follows : 



, , The Thompson limestone is gray and somewhat shaly, and on its weathered surface in 

 placfii^.are round, oblong, or irregular patches of darker, more or less granular calcite, which at 

 once suggests fossils, though their specific determination is a matter of difficulty. Where shaly 

 it is generally red, highly argillaceous, and locally full of long, slender gastropods, which weather 

 out and leave tlje porous argillaceous skeleton of the limestone full of "screw holes." * * * 

 The relation of the Thompson limestone to the meta-andesite that bounds it upon the west may 

 be clearly seen on the northern slope of Mount Jura, near the end of the lime road, where the red 

 calcareous beds, full of slender gastropods, come into direct contact with the altered andesite. 

 The fossils lie parallel to the surface of the volcanic rock, practically against it, without showing 

 any alteration due to the presence of the igneous rock. This relation evidently indicates that 

 the Hmestone was deposited upon the meta-andesite and is of later age. It has already been 



