CORRELATION OF STRATA. xcill 
fauna pass on into the next bed or reappear in one or the other of the succeeding beds. 
If, however, we examine these species we notice that of the 42 forms which it holds in 
common with later divisions at least twelve species of Bryozoa, Brachiopoda and Trilobita 
range through three or more groups, and therefore ought not to be taken into account in 
determining the question under consideration. Deducting these the percentage of species 
passing upward is considerably reduced, while the remaining fauna is more in accordance 
with that of the preceding limestones. As itis, over half of the entire fauna is received 
from below. 
In comparing the Stones River group as developed in Minnesota with equivalent rocks 
at other localities embraced within the limits of the Upper Mississippi province, we find 
that the lithologic characters change towards the east and south. Thus at Beloit, 
Wisconsin, and at Rockton, Illinois, the Lower Buff and Lower Blue limestones are more 
nearly alike in texture and composition than is the case farther west in those states. In 
the quarries at Rockton these beds as well as the Upper Buff limestone are enough alike 
to have been considered by Whitney and Worthen as the same as what the Wisconsin 
geologists have more recently distinguished as the Lower Buff. At Mineral Point, 
Wisconsin, and Dixon and Dunlieth, Illinois, the Lower Blue is a pure limestone and 
readily separated from the Lower Buff. In Minnesota, however, the strata equivalent to 
the Lower Buff are a purer limestone than usual in the northwest, while the strata which 
we parallelize with the Lower Blue are magnesian in the middle member (Vanuxemia bed), 
clayey in the lower, and an alternation of pure crystalline limestones and shales in the 
upper. 
The Trenton period of the northwestern states may be divided into three regions in 
each of which the lithologic character of the various beds is approximately uniform, 
namely, the Minnesota area, the region included between the three towns of Dixon, 
Dunlieth and Mineral Point, and the third including the towns of Janesville, Beloit and 
Rockton. In the first, the period includes much shale, in the second, a good proportion 
is pure limestone, in the third, all the beds are more or less distinctly dolomitic. These 
lithologic areas, if we may so call them, of course merge gradually into each other, and 
probably are due to conditions depending upon the distance of each area from the Lower 
Silurian shore line. 
Of Wisconsin sections of the group of strata under consideration, the one which, so 
far as known to us, offers the greatest resemblance to the St. Paul section, occurs near 
Benton, Wisconsin. Here the ‘‘Lower Blue limestone” is terminated above by two beds 
corresponding in position and fossils, and fairly well also as regards composition, to the 
Vanuxemia and Stictoporella beds. 
In central Kentucky the rocks which belong to this group form precipitous bluffs, 
often over two hundred feet in hight, along the Kentucky river from Frankfort to and 
beyond High Bridge. Nearly the whole of this section consists of massive dove-colored 
limestones, exceedingly like and unquestionably equivalent to the Birdseye limestone of 
New York. The base of the group is not exposed in Kentucky so that we have only the 
