24 The American Geologist. January, 1894 
strata from lake Michigan to lake Superior, he represents the 
rocks of the Penokee iron ridge as dipping northward, hut 
rising again before reaching lake Superior, their northern out- 
cropping edges being hid by the horizontal sandstones. The 
St. Croix sandstone is described under the name Potsdam 
sandstone. The Lower Magnesian limestone he considered the 
equivalent of the Calciferous sandstone of New York. The 
St. Peter's sandstone has a thickness of about 100 feet, but 
is "concealed by overlying rocks" to the eastward of its line 
of outcrop, its most northern known outcrop being in Sha- 
wano county. The Butt' and Blue limestones (with the Ga- 
lena) he puts in the Trenton period, and conformable on the 
St. Peter sandstone. The interesting remark is made that 
these beds embrace a "layer of highly bituminous shaly lime- 
stone, often so well saturated with bitumen as to burn with a 
blaze." This fact was discovered in Minnesota about the 
same time, and it shows, as remarked by Lapham, an abun- 
dant display of low forms of plant-life over a wide continental 
area in Lower Silurian time.* The Galena limestone, the Cin- 
cinnati group, the Clinton and the Niagara are mentioned. 
He also adds here, to the Upper Silurian the Racine limestone 
and the Salina, the latter occurring at a single locality on 
Mud creek, near Milwaukee; but fragments found in the 
drift indicate a much greater extent of this rock. It had been 
the source of small quantities of gypsum and of salt. Of the 
Devonian he adds to previous statements, the "Black Shale." 
which is found in considerable quantities distributed in the 
drift northward from Milwaukee. 
His brief paper in 1874. on the relation of the Wisconsin 
geological survey to agriculture, contains a concise statement 
of those ways in which geology bears directly on the interests 
of the farmer, and is designed to recommend the new survey 
to the favorable attention of such legislators as were from the 
rural districts. It was read before the State Agricultural So- 
ciety. The distribution and nature of the drift which deter- 
mines the distribution and nature of the subsoils, the ascertain- 
ment of nights and depressions, on which depend the surface 
drainage and the depths to subterranean streams, and hence 
*It is apparently the same as the stratum described by J. D. Whitney 
as Utica slate in Iowa. Geology of Iowa, Vol. i, pp. 359-60, 1858. 
