Geology of the St. Croix Dalles. — Bcrkey. 275 
Dicellocephaliis barabucnsis Whitfield. 
D. etoni Whitfield. , 
Illcouirus coiiiiexus Whitfield. 
Chapter II. Additions to the Fauna. 
The greater part of tlie sedimentary strata in this area is 
made up of porous friable sandstones and shales unfavorable 
for the preservation of organic remains. Calcareous portions 
of the lower Dresbach shales are, however, favorable for pres- 
ervation and in them are crowded great numbers of Lingu- 
lepis piniiiforniis and related forms. Certain portions of the 
green-sand horizon also are packed with the broken fragments 
of shells. Although fragments are so abundant it is almost 
impossible to obtain specimens from the green-sand bed suffi- 
ciently well preserved to be identified. Portions of the finer 
grained sandstones still preserve the imprints of numerous 
forms, although in most cases no trace of the original shell 
remains. These occurrences are always limited in extent, and 
consequently in many outcrops they are not to be found at all. 
One of the most promising localities for fossils is Lawrence 
creek gorge at Franconia, from which several good fossilifer- 
ous slabs were taken. The marginal conglomerates have 
proved most fruitful, and recently a fauna has been discovered 
in these conglomerates which is unique. Several new' species 
and a few rare types are included in it. The general character 
of the fauna is essentially that represented in the Baraboo 
fossils described by Whitfield in Geology of Wisconsin (loc. 
cit.). Over a hundred specimens have been obtained and 
the range of variability which they exhibit throws some lignt 
upon classification of the early forms of gastropods. The 
gastropods are almost wholly of the conical type with oval 
aperture. They thus belong to Tryblidium and related 
genera. 
Principles of Classification. — Of the total number of spe- 
cies credited to the Cambrian, 65 per cent belong to the dis- 
tinctly conical shells. Moreover twenty species of cone- 
shaped mollusks classed with the Pteropoda are placed in the 
Cambrian, so that of the whole number of species of all re- 
lated forms. 80 per cent are distinctly conical in outline. In 
accordance with evidence gathered from the descriptions of 
