3 1 6 The American Geologist. November, isns 
is doubtless unnecessary. This paper has to do with the equiv- 
alent or continuation of the Trenton group in the upper Miss- 
issippi basin, especially at St. Paul, Minnesota. To explain 
briefly: the Chazy formation, the Trenton including the Black- 
River formation and the Hudson formation including the Uti- 
ca of New York are, as is generally recognized, represented 
in this area by three divisions, the St. Peter sandstone, the Gal- 
ena series and the Maquoketa series respectively. It is still 
somewhat indeterminate whether the Trenton stage compris- 
ing the formations or divisions just mentioned, has all its sub- 
divisions represented in the upj^er Mississippi basin. The 
Trenton stage is very thick in the New York region while the 
equivalent here is thin, not exceeding 400 feet. Yet a com- 
plete sequence of beds would appear to be developed in both re- 
gions and the much thinner western representative is probably 
not to be considered as an incomplete one, but rather each sub- 
division there may have its coordinate here. This hypothesis 
accords further with the great uniformity and wide extent of 
each bed of this stage in the" Northwest. In a former article,* 
I have endeavored to show how the several parts of the Galena 
and the Maquoketa series are nearly coextensive over their 
known extent, but I was not able to describe an exact relation 
between the Trenton stage of New York and that of the 
Northwest, because the necessary store of evidence for such 
an undertaking is not at hand. A few data only were con- 
tributed on the deposits here. Ruedemann,f WhiteJ and Pros- 
ser and Cumings§ have materially increased our knowledge 
of the New Yot^k Trenton stage deposits in recent articles. 
Ruedemann describes especially evidences of oceanic cur- 
rents in the Utica formation and again similar evidence from 
conglomerates in the Trenton formation. Although it may 
be very little known to geologists, yet conglomeratic zones 
exist in the Galena (Trenton) series in Minnesota and Wiscon- 
sin, and evidence of marine erosion or corrosion recurs in it 
at several horizons. These zones, moreover, appear to mark 
the divisions between successive faunal and stratigraphic beds, 
^American Geologist, vol. 18, p. 357: vol. it), p. 21. 
tAmerican Geologist, vol. 21, p. 75; vol. 19. p. 367. 
JTrans. N. Y. Acad. Sci., vol. 15, p. 71. 
§Fifteenth Ann. Rep. N. Y. State Geologist, p. 619. 
