OORKKI.ATION OF STRATA. 



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 lau-r divisions at least twelve species of Bryoeoa, Brachiopoda and Trilobita 

 rnn^e through throe <>r inon- irmups. 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 

 wall that of the preceding limestones. As it is. 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 Kockton, 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 quar ;ockton 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 ceutral Kentucky the rocks which belong to this group form precipitous bluffs, 

 often over two hundred feet in bight, 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 



