314 
IOWA CAMBRIC SUCCESSION 
exposed along the bluffs of the Mississippi River, between Dubu¬ 
que and St. Paul; and thereby to adjust some of the previously 
disconnected observations in this region. During the summer 
before, a brief trip was made along the line of the Chicago, Mil¬ 
waukee and St. Paul railway, from La Crosse, through Sparta 
and Tomah, to Portage. Years before the sections about Madi¬ 
son were examined; and the Minnesota River outcrops were also 
noted in some detail. Recently the last mentioned localities were 
reviewed anew. The conclusions reached are briefly summed up 
in the accompanying notes. 
From a strictly historical angle the Cambric section under 
consideration has an especial interest for reason of the fact that 
it was part of that exposure where modern stratigraphic correla¬ 
tion by means of contained organic remains was first introduced 
into this country from England. This accomplishment was the 
effort of Thomas Nuttall, who, in the summer of 1809, made a 
canoe voyage from the mouth of the Wisconsin to the mouth of 
the Missouri River.^ Nuttall, although primarily a botanist and 
ornithologist, garnered plentifully of the fossils which came in his 
way on the trip. These he later studied carefully and compared 
with the then recent descriptions by Martin of the fossils of the 
Derbyshire district of England. Since the majority of his own 
collections were from the rocks now known as the Mississippian 
limestones, of Early Carbonic age, he naturally found Ameri¬ 
can forms closely related, if not identical with, the English 
species.^ 
This northeastern Iowa section happens, also, to be among the 
first identifications on the American continent of Murchison’s Silu¬ 
rian system. While the New York geologists of that day were 
busily engaged in attempts to establish a “New York System,” 
comparable with Murchison’s Siluria and Sedgwick’s Cambria. 
Owen* was patiently and properly fitting the rocks of the Upper 
Mississippi basin to the newly established English scheme. 
Nuttall’s determinations of the rocks of the Mississippi bluffs 
to be the equivalents of the Mountain limestones (Early Carbonic) 
farther south had a curiously aberrant influence upon subsequent 
2 Jour. Acad. Nat. Sci., Philadelphia, Vol. II, pp. 14-52, 1821. 
3 Pop. Sci. Monthly, Vol. LXXXIV, p. 184, 1914. 
4 Twenty-eighth Cong., 1st. Sess., Sen. Ex. Doc. Na 407, 145 pp., 1844. 
