26 The American Geolof/ist. January, i897 
nectioii with the stiiitigrapliic depcriptidns because they en- 
tail too much discussion to permit of their insertion here. 
For the study of both migratory and evolutionary history 
of the species the division into formatio7is is of less value 
than that into beds, because detail is essential. And since 
the purpose of the writer as paleontologist is primarily to es- 
tablish a complete and uniform scheme of classification of the 
Galena and Maquoketa series for further use in the study of 
the organic remains and the conditions under which the 
abundant fauna of these deposits lived, detailed descriptions 
of the beds will be undertaken. An earlier attempt* toward 
that end is now repeated in part but in corrected and more 
complete form. The average thickness of some of the beds as 
given is emended, the Zygospira bed is included in the Orthis- 
ina bed, and the new name, Triplecia bed, stands for that 
which was before erroneousl}^ called Maquoketa shales, and 
the true Maquoketa formation is placed where it belongs. In 
the section near Spring Valley, Minnesota, the true Maquo- 
keta formation is wanting between the Triplecia bed and 
Wykotf beds, and hence the mistake, for, having found tlie 
fauna of the Orthoceras bed in some small isolated exposures 
several miles farther south, it was supposed to belong to an 
upper Wykolf bed because it did not belong to the known 
section, while clearly belonging near the same. This mistake 
has remained already too long uncorrected, and strangely 
other writers have independently fallen into the same error. 
1. Buff limestone bed. 
The Buff (Lower Buff) limestone lies conformably upon the Saint 
Peter sandstone, from which it is separated generally by an abrupt 
transition from sand to clay or shale. The clay stratum, three feet or 
less in thickness, is apparently an altered portion of the regular lime- 
stone and contains Buff limestone fossils only. When wanting, an im- 
pure sandstone belonging to the Saint Peter may seem to take its place. 
The limestone bed itself is heavily and regularly stratified. 
The lamination, when evident, is irregularly lenticular, from uneven 
distribution of impurities. f The stone is then very little dolomitic. In 
many localities the lamination has been nearly all obscured by altera- 
tion and a porous, more dolomitic limestone, or in other cases, a com- 
pact crystalline limestone has resulted. In the last named condition 
*Bull. Minn. Acad. Nat. Sci., vol. in, p. 319. 
tSee Bull. Minn. Acad. Nat. Sci., vol. in, p. 119, and pi. 1, hg. 1, C. 
W. Hall (1889). 
