364 The American Geologist. December, i8fG 
Tronton Shales, N. H. Wiiicholl (1888). Geological and Natural His 
tory Survey of Minnesota, Final Report, vol. II, p. 288, 356. 
This term Trenton Shales ought perhaps to be treated as a synonynj 
for Green Shales, which it is in general, although the application of the 
term makes it include more strata than under the old term. 
The Galena series has also been divided into two parts in a 
different manner from the above, and the first division, under 
the name Trenton, contained the Lower Trenton, Green Shales 
and Upper Trenton, and the second was called Galena. Al- 
though the division was probably intended to he the same as 
that in Iowa and Wisconsin under the. same name, it is so 
much different that a separate heading is required. 
"TRENTON," 
Trenton limestone, N. H. Winchell (187.'J). Geological and Natural 
History Survey of Minnesota, 1st Annual Report, p. 92. 
Trenton limestone, M. W. Harrington (1876). Geological and Natu- 
ral History Survey of Minnesota, 4th Annual Report, p. 90, 111. 
Trenton limestone, N. H. Winchell (1877). Geological and Natural 
History Survey of Minnesota, 5th Annual Report, p. 25 and 147. 
Trenton limestone, N. H. Winchell (1884). Geological and Natural 
History Survey of Minnesota, Final Report, vol. I, p. 370. 
The term Galena, as used co-ordinate with this last exten- 
sion of the term Trenton, includes only the upper part of the 
Galena proper. 
"galena." 
Galena limestone, N. H. Winchell (1874), Geological and Natural 
History Survey of Minnesota, 1st Annual Report, p, 104. 
Galena limestone, M. W. Harrington (1876). Geological and Natural 
History Survey of Minnesota, 4th Annual Report, p. 91. 
Galena formation, N. H. Winchell (1884). Geological and Naturaf. 
History Survey of Minnesota, Final Report, vol. I, p. 334, 371. 
In one instance the term Upper Trenton is used to include 
the Galena exclusive of the "Galena" as given above. 
Upper Trenton, N, H, Winchell (1884), Geological and Natural His- 
tory Survey of Minnesota, Final Report, vol, I, p. .334, 
Except as just described, the division of the Galena forma- 
tion has not been attempted until very recently. And it seems 
possible that the separation into "Upper Trenton," as given, 
and "Galena" was due to mistake and that the intention was 
to make the same division in Minnesota as in Iowa and Wis- 
consin. 
The Galena formation, as a grand division of the Galena- 
Trenton series and co-ordinate witli the Beloit or "Trenton"' 
