162 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



and is at many places full of fossils, especially of several species of Prodiiclus, 

 from which fact it is often called the ' Prodiidus limestone.' Not far to the north, 

 in the Swan Lake district, the upper limestone is replaced by siliceous or cherty 

 shale of dark-purplish color. This cherty shale is not as a rule a prominent 

 feature of the stratigraphy nor does it at many places contain fossils. 



"The lower limestone in the Montpelier region is of a whitish or buff color 

 and at some places appears to be a fine-grained calcareous sandstone rather than 

 a limestone. As a rule its fossils are very few and so ill preserved as to be indeter- 

 minable. In the Swan Lake district, on the other hand, this bed is a massive 

 whitish, more or less siliceous limestone containing in abundance poorly preserved 

 silicified fossils, among them species of Spirijer, Squamularia, and probably 

 Composita. In its upper portion a large semireticulate Produdus is found, and 

 fine, black, earthy limestones that locally appear at its very top contain numerous 

 specimens of Spirijer, Produdus, and Composita. In this region the lower lime- 

 stone ser\^es much better than the upper as a guide for finding the phosphate 

 beds, and for several reasons, more or less obvious, it seems to have been generally 

 inferred that the guide rock w^as the same in both areas and that the series was 

 overturned in the Swan Lake region. There is, however, hardly room for reason- 

 able doubt that the stratigraphic sequence is normal in both regions and that the 

 beds themselves differ in character in the two areas. 



"The phosphate beds consist mosdy of soft rock, shales, phosphates, and 

 impure limestones, the latter seldom more than a few inches thick. The shales 

 are more or less phosphatic and the phosphate bands are more or less argillaceous. 

 Their prevailing color is black, weathering to brown, but in the Beckwith Hills 

 the color of the phosphate and associated rock is buff or even reddish. The 

 thickness of the phosphate-bearing shales ranges from 60 to 100 feet._ The main 

 deposits of phosphate occur, as a rule, at the base of the series, so that in the Mont- 

 pelier district they lie about that distance below the 'upper Produdus limestone,' 

 but in the Swan Lake district they occur immediately above the ' lower Produdus 

 limestone.' 



"The remaining formations concern the present report less closely. The beds 

 below the Park City formation in southern Idaho have been identified with the 

 Weber quartzite, which holds a similar position in the Wasatch Range. The 

 equivalence of the strata in the two sections, especially in detail, is not entirely 

 clear. In Idaho the 'lower Produdus limestone' abruptly grades below into 

 white sandstones and quartzites, and the Mississipplan limestones are succeeded 

 above by light-colored limestones that include more or less interbedded quartzitic 

 sandstones, these being probably of Pennsylvanian age. Between these two 

 quartzite-bearing groups comes in a series of soft beds approximately 1,000 feet 

 thick. They are poorly exposed, but seem to comprise soft sandstones and soft 

 earthy limestones of reddish or yellowish tints. If the upper quartzitic beds are 

 called the Weber, the division between the Weber and the Park City is not easy 

 to determine. It may prove desirable to draw the line at the base of the phos- 

 phate shales and to include the siliceous limestones and calcareous sandstones of 

 the ' lower Produdus limestone ' in the Weber. If so, the thin stratum of black 

 limestone which at some places occurs at the base of the phosphate beds and has 

 here been spoken of as part of the 'lower Produdus limestone' may perhaps 

 better be united with the Park City formation, because the fossils obtained in it 

 indicate a certain change from the fauna of the white limestone below and an 

 affinity with the fauna of the phosphate series above. In any event, the Weber 



