XCV111 THE PALEONTOLOGY OF MINNESOTA. 



York and Canada. That this is a fact, is, we think, shown beyond any question whatever 

 by the summary tables following the list of fossils. As given there no less than 107, or 87 

 per cent, of the 123 species common to the Galena of the northwest and one or more of the 

 four other regions compared, occur elsewhere in the Trenton group. This percentage is 

 increased to nearly 95 per cent., if we consider only the species that are restricted to the 

 group in the northwest, since of 76 of such species 72 occur elsewhere in the Trenton group. 

 That the Galena is a distinct group by itself is we think again shown conclusively by 

 summary table No. 1. This gives a total of 305 species, of which 227, or about 74 percent., 

 are restricted to the group. 



The Trenton group everywhere is a limestone, usually thin bedded and with more or 

 less of shale in the lower part, and thick bedded and coarser textured in the upper. 

 Sometimes, as at Frankfort and Covington, Ky., and Nashville, Tenn., there is some shale 

 also near or at the extreme top. In the eastern states the lower part is black, the upper 

 dark gray; south of the Ohio river both divisions are of lighter shades, the lower part 

 being dark gray or blue, the upper a light gray or dove-color and when shaly a darker 

 gray or blue; in the northwest the~whole may be of various shades of buff, or the lower 

 half may be in parts yellowish, grayish or with faint blue or greenish tints. 



In the northwest, if the group is traced from southern Wisconsin into Illinois and then 

 around the supposed upper Mississippi barrier into Iowa and Minnesota, a gradual change 

 in the lithologic characters of the group will be noticed. In the first locality the Trenton 

 or Galena is a dolomitic limestone throughout, in Illinois it sustains very little if any 

 change, but in Iowa, as for instance at Decorah, the basal part is decidedly shaly and 

 contains some layers of nearly pure limestone. In Pillmore county, Minnesota, the pure 

 limestone has increased very materially in thickness, over 100 feet being of this character 

 at Wykoff, leaving only about 50 feet at the top (the Maclurea bed) retaining the dolomitic 

 feature that pertains to the whole of the group in southern Wisconsin. In following the 

 group through Olmsted county into Goodhue we observe that now the lime also is 

 gradually replaced (from the bottom upward) by more and more of argillaceous material, 

 so that in the last county, between the post offices of Hader and Holden, only about 20 

 feet at the top of the Fusispira bed is still a pure limestone. Only a few feet of the 

 Maclurea bed is left in Goodhue county and this seems to be essentially of the same 

 character as in Fillmore county. North of Goodhue county all of the Trenton, save the 

 lowest member (Clitambonites bed ) has been swept away, so we cannot say positively that 

 the Maclurea bed, like the Fusispira bed, was eventually also replaced by shales. 



In Minnesota the group is divisible into three or four beds as follows: 



Clitambonites bed. This division (see sections 1, 2 and 3) consists of yellowish, light 

 green or drab shales, with more or less of thin, indurated clay or impure limestone layers 

 in the lower two-thirds, At the top there is a bed of light shale without hard layers, five 

 to ten feet in thickness, in which fossils are very scarce. In the remainder, however, 

 fossils are exceedingly plentiful, and, excepting the Mollusca, very well preserved. The 

 whole bed is from 15 to 22 feet thick at St. Paul and in Goodhue county. Like the 



