100 Wisconsin Academy of Sciences, Arts, and Letters. 
and siliceous rock meal interbedded or irregularly mixed with 
quartz sand and fine siliceous clay-like deposits, locally attaining an 
aggregate thickness of nearly 200 feet and all derived from the sur¬ 
face wear of older formations to the north. The distribution of 
this basal St. Peter conglomerate suggests long continued work of 
streams of considerable size. In short, the physical data now in 
hand clearly establish the propriety of Ulrich’s proposal to draw 
a systematic boundary between the top of the Shakopee and the 
base of the St. Peter in the Upper Mississippi Valley and at the 
corresponding everywhere easily identified plane elsewhere in 
America. Out of the hundreds of species of fossils found on the 
two sides of this stratigraphic break not a single one passes across 
the line; and of the Canadian genera many less than half their num¬ 
ber are recognized in the succeeding Ordovician faunas. Besides, 
this restriction of the Ordovician system still leaves it with an 
aggregate thickness of deposits exceeding the average for most of 
the systems now recognized. 
The Canadian-0zarhian break. —In the Upper Mississippi Valley 
this break commonly lies within the mass of dolomitic limestone 
that up to ten or fifteen years ago was generally known as the 
Lower Magnesian limestone. More recently the locality term 
Prairie du Chien limestone or formation was ill-advisedly proposed 
to replace the lithologic name. Before that McGee^^ working in 
northeastern Iowa proposed the name Oneota for the lower part of 
the mass and WinchelP® gave the name Shakopee to what we now 
know as its upper part. A sandstone believed to lie between the 
two was called New Richmond sandstone by Wooster.-^ Because of 
the formerly prevailing belief that these three divisions are coex¬ 
tensive much confusion has attended their identification from place 
to place in Iowa and Minnesota. In Wisconsin, following publica¬ 
tion of Wooster’s work in 1882, practically no published attempt' 
has been made to distinguish the divisions. 
The field work of the writer in Wisconsin and adjoining States, 
particularly during the past ten years, has demonstrated that' the 
Shakopee is unquestionably distinguishable from the Oneota dolo¬ 
mite throughout their extent in the Upper Mississippi Valley. The 
evidence respecting the New Richmond sandstone is much less sat¬ 
isfactory. It is evident not only that this dolomitic series embraces 
U. S. Geol. Surv., 11th Ann. Rept., pt. i, p. 331, 1891. 
>2® Minn. Geol. and Nat. Hist. Surv., 2d Ann. Rept., p. 138, 1874. 
Geology of Wisconsin, vol. IV, pp. 106 and 127, 1882. 
