:WN The American Geologist. November, 1868 
crystalline, but a distinctly fragmental rock, remarking that Irving 
placed it in the Huronian, a terrane from which Irving specially ex- 
cluded crystalline rocks (excepting such as are eruptive in the Huron- 
ian). He refers to Winchell's having considered it Potsdam, but 
seems to understand that Winchell's Potsdam is "upper Cambrian," 
whereas if there be anything which Prof. Winchell has maintained re- 
specting the Potsdam, i. e., the Potsdam at Potsdam, N. Y., it is that it 
is not upper Cambrian, but much older, and unconformable below the 
upper Cambrian. There has been great confusion in the use of the 
term Potsdam because of its having been applied erroneously to two 
widely different formations, both in New York state and Vermont, and 
in the Northwest. This confusion, which culminates in a single sen- 
tence on p. 17, is increased by all such as persist in putting into the 
Potsdam such beds as those at Saratoga, N. Y., containing an upper 
Cambrian fauna I well known long as a characteristic locality for the 
New York Calciferous), and such beds as the St. Croix, in the west, 
which contain a similar fauna, since no such beds, nor such a fauna 
are found at Potsdam, N. Y., but only such as exist in the 
Sioux quartzyte. Winchell regards the true Potsdam as a part of the 
true Huronian. and the true Huronian as a synonym of the Taconic. 
and the whole, of course, as "lower Cambrian,'" as that term is defined 
by Walcott. Those strata to which the term Potsdam has also been ap- 
plied, belonging to the "upper Cambrian,"' containing the Dikelloce- 
phalus fauna, are separated everywhere from the true Potsdam by a 
great non-conformity. The misfortune has been that this non-conform- 
ity has never been identified fully in the immediate vicinity of Potsdam, 
and was wdiolly unknown and unsuspected until the wider relations and 
extension of the two formations were studied. It is now known in 
Vermont, in eastern New York, New Jersey, Pennsylvania, Michigan, 
Wisconsin and Minnesota. It also occurs in the Black Hills, S. Dak. 
This break separates the upper Cambrian from the lower, or, more cor- 
rectly, the Cambrian from the Taconic. 
Mr. Keyes, however, is "at home'" in the description of the Carbonifer- 
ous. He gives important illustrated sections of the stratigraphy of the 
Coal Measures of Central Iowa, taken along the line of the Des Moines 
and Raccoon rivers. He illustrates a marked non-conformity between 
the Coal Measures and the St. Louis limestone. The lower or calcare- 
ous member of the Carboniferous he styles the "Missi6sippian series,"' 
and this includes the Kaskaskia, St. Louis, Augusta and the Kinder- 
hook limestones, while the "Pennsylvanian series" takes in all the Coal 
Measures. He affirms that in the overlap of the Coal Measures over 
older rocks the shore line passed over Lower Carboniferous, Devonian, 
and even Silurian rocks, which had formed an ancient surface, with 
hills and vales, ridges and gorges. This general submergence was 
followed by many minor oscillations, producing great and sudden vari- 
ations in the lithology of the cotemporaneous strata. 
Prof. Calvin, in his discussion of the Cretaceous of Woodbury and 
Plymouth counties, regards the chalk (Niobrara), the shales (Fort 
v 
