Cll THE PALEONTOLOGY OF MINNESOTA. 



say that our preference is dominated by a sense of its utility and fitness. There is no 

 other locality on the continent that deserves so well to be considered the typical locality 

 for the series of strata in question as the region about Cincinnati, Ohio. All the groups 

 into which the period may be divided are well represented there, and when it comes to 

 their faunas and the facilities for collecting fossils, there is no other region in America 

 where the fossils are so plentiful and so easy to obtain. Throughout this volume, however, 

 and in all the Minnesota reports the term Hudson River has been used, and it is only from 

 a sense of consistency that it is placed first in our title. 



Only a brief account of the subdivisions of this important series of rocks will be 

 attempted here, the point of chief interest to students of northwestern geology being the 

 determination of the exact equivalents of the two Minnesota divisions of the formation in 

 the Cincinnati section. 



The strata of the Cincinnati period as exposed in Ohio, Indiana and Kentucky, are 

 divisible into three groups, having about the same geological value as the Chazy, Stones 

 River, Black River, and Trenton groups of the Trenton period, and the Medina, Clinton 

 and Niagara groups of the Niagara period. These three divisions correspond very nearly 

 with the Lower, Middle, and Upper Hudson of the Kentucky geologists, and the Eden 

 shales, Hill Quarry beds, and Lebanon beds of Prof. Edward Orton in Vol. I, Geology of 

 Ohio. 



At Cincinnati we begin the period with the Utica group, which here consists of over 

 250 feet of grayish and blue calcareous shales and marls, in which many layers of 

 more or less crystalline limestone, from one to twenty inches thick, are included.* The 

 lower 15 or 20 feet of this division are of a darker color than the succeeding shales, being 

 greenish gray or drab rather than light blue. It is this portion that agrees best in all 

 respects with the Utica of New York and Canada, and it was so determined by Prof. James 

 Hall as early as 1842. The gray shales contain more or less abundantly such widely 

 distributed and characteristic Utica fossils as Triarthrus becki, PrimUiella unicornis, 

 Leptobolus insignis, Lingula daphne, Dicranograptus ramosus, Diplograptus spinulosus, 

 D. putillus, Dendrograplus simplex and D. tenuiramosus. Of these, the last three, as well 

 as many other species, continue into the main body of the shaly strata of the group. 

 Throughout, fossils, Bryozoa especially, occur in greater abundance, variety and perfec- 

 tion than at any other known locality for the Utica. At the top the shales pass rather 

 gradually into the "Hill Quarry beds." 



The latter, for which we propose to use the name Lorraine group, are clearly equiva- 

 lent to the greater part of the New York strata which Emmons included under that name.f 

 At the base of the division, which at Cincinnati comprises about 200 feet of strata, there 

 are some arenaceous layers that on weathering frequently preserve the fossils as casts. 



At Cincinnati, as may be seen opposite the city In the Kentucky bank of the river between the towns of West Onv- 

 Ington and Ludlow, the Utica rests on at least 50 feet of limestones and shales belonging to the Trenton group. The latter 

 terminate above with a heavy current-formed crlnoldal layer, which Includes large pebbles and disturbed masses of the 

 underlying limestone layers and exhibits other evidences of unconformity by erosion between the two periods. 



+ We refer particularly to Emmons' Lorraine sandstone, the greater part, if not all, of his Lorraine shales, which 

 Walcott In 1879 referred to the Utica, being probably equivalent to the upper part of the Utica at Cincinnati. 



