Clv 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 Tefradium minus Safford and Protarea 
velusta Hall, two Trenton species; while the following Trenton types, Strophomenu 
filitexta, S. trentonensis, S. trilobata and Rhynchotrema increbescens are represented 
respectively by S. neglecta, S. rugosa, 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, anil 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 partof this seems to belong to the Richmond group. 
The Utica group also is probably wanting entirely in the northeastern corner of 
Illinois, but in the northwestern corner at Savannah, where the whole period is little léss 
than 100 feet thick, the lower 50 feet belong to this group, while the upper represents the 
Richmond group. From a paper by Prof. J. F. 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 
lowa 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 
east-northeast 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 Hyolithes parviusculus and Coleolus 
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 Plectambonites 
sericea, Orthis testudinaria, varieties mullisecta 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, Leptobolus 
oceidentalis and Diplograptus putillus. 
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, 6; 1890, 
