CIV THE PALEONTOLOGY OF MINNESOTA. 



upper Trenton species, while C. halli Nicholson, of which the typical form occurs in the 

 Stones River and Black River groups, recurs here as well as at the top of the Trenton in 

 slightly modified forms. Then we have varieties of Teiradium minus Safford and Proiurea 

 vetusta Hall, two Trenton species; while the following Trenton types, Sirophomena 

 filitexta, S. trenionensis, S. trilobata and Rhynchotrema increbescens are represented 

 respectively by S. neglccta, S. rugosu. S. nutans and R. capax. And all these species, 

 moreover belong to the predominant fossils of the group. Still, of the total number of 

 species known from the group (over 300) nearly three-fourths are restricted to it. 



Only two of the groups of the Cincinnati period are represented in Minnesota, viz: 

 the lower and the upper, an I both by but a small thickness. The Lorraine group thins 

 rapidly in a northwestward direction from Cincinnati, and probably runs out altogether 

 before reaching Kankakee, Illinois, where the volume of the whole period is less than 250 

 feet; and much the greater part of this seems to belong to the Richmond group. 



The Utica group also is probably wanting entii-ely in the northeastern corner of 

 Illinois, but in the northwestern corner at Savannah, where the whole period is little less 

 than 100 feet thick, the lower 50 feet belong to this group, while the upper represents the 

 Richmond group. Prom a paper by Prof. J. P. James* it appears that the Cincinnati period 

 occasionally exceeds 100 feet in thickness in Iowa, but on the whole it diminishes slowly 

 northward from the latitude of Savannah. 



The Utica group in the Northwest seems to be a relatively deep sea deposit, and, in 

 Iowa in particular, probably represents, so far as time is concerned, not only the Utica but 

 the Lorraine of the Cincinnati region as well, without however at any time receiving any 

 of the characteristic fauna of the latter. 



The Lorraine deposits and fauna of the Cincinnati province were derived from the 

 easUnortbeast and for some reason (perhaps deep water) did not extend into the northern 

 Mississippi province. At the beginning of the Richmond group the Cincinnati province 

 received an incursion of northwestern species like Hyolithcs parviusculus and Colcolus 

 iowensis James. 



In Minnesota the Utica group (see section 8) rests on the unevenly laminated, bluish- 

 gray, crinoidal limestone, which forms the top of the Trenton, and consists of 20 feet or 

 more of layers of impure, evenly bedded, compact gray limestone, varying from 2 to 12 

 inches in thickness, separated by thin seams of shale. In the upper part of this bed the 

 limestone layers are prevailingly thinner than in the lower part, and contain an abundance 

 of small specimens of Asaphus megistos. The interbedded shales contain I'lectambonites 

 sericea, Orthis testudinaria, varieties multisecta and emacerata, Triplecia ulrichi and a 

 number of undetermined Bryozoa, while about 14 feet above the crinoidal limestone one of 

 the layers furnished numerous specimens of several species of Lingula, Leptobolns 

 occidentalis and Diplograptus puiillus. 



The above describes the beds and fauna of the group as it is exposed in the vicinity of 

 Spring Valley. Farther south, between Granger, Minn., and Graf, Iowa, the fossiliferous 



* American Geologist, vol. 5. no. 8; I860, 



