LIMESTONE FORMATION OF LECLAIRE, etC. 307 



colored limestone, bearing Halysites catenulatus, Fentamerus oblongus, and 

 many large Orthoceratites, which are everywhere regarded as evidence Ot. 

 the Niagara age. I could not hesitate, therefore to parallelize the suc- 

 ceeding beds with the limestone of Leclaire, though we had failed to 

 trace it across the country in a continuous outcrop. At the same time, on 

 critical examination of the collection of fossils made at Racine and at 

 some other points, I detected many species known as characteristic of the 

 Niagara formation in the State of New-York, requiring its recognition as 

 a member of that group (rather than of the Onondaga-salt group), and 

 uniting with it as identical in position the Leclaire limestone.* 



At the same time, we have recognised from Racine and adjacent locali- 

 ties, including Leclaire in Iowa and a single locality in Illinois, the fol- 

 lowing species which are identified or very closely allied to those from 

 Gait in Canada West : Fentamerus occidentalism an Obolus-like fossil, a 

 Favosites and a species of Amplexus which are identical in several locali- 

 ties, Cyclonema sulcata, Murchisonia logani, Murchisonia identical or close- 

 ly allied to M. mylitta ( Billings ), an undescribed Murchisonia from 

 Racine identical with one from Gait, Subulites ventricosa, Fleurotomaria 

 solaroides ? Loxonema longispira, besides other forms which are closely al- 

 lied to species of the Guelph limestone. 



An examination of several localities in Wisconsin shows that this pecu- 

 liar fossiliferous limestone is very unequally distributed. At Racine it 

 has a very considerable thickness ;t while in other places, either from 

 denudation or other causes, it is very thin, or even absent. In some places 

 in the vicinity of Milwaukee and Waukesha, there are indications of beds 

 of passage from the regularly bedded limestones below to the unequally 

 bedded rock above. There appears indeed very good evidence of the ir- 

 regular or unequal accumulation of this higher rock in many of the loca- 

 lities along a considerable portion of the outcrop ; and where the lower 

 part of the formation comes to the surface, the upper rock does not appear 

 to be developed. I am therefore induced to believe that this limestone at 

 Racine, the mass at Leclaire and extending thence into Iowa, as well as 

 the Guelph formation in Canada and the feeble representation of the same 

 in New-York, are really lenticular masses of greater or less extent, which 

 have accumulated upon the unequal surface of the ocean bed in a shallow 

 sea during the latter part of the Niagara period. These isolated masses 

 of limestone have close relations with each other, while their relations with 

 the Onondaga-salt group, though very intimate in the single locality in Cen- 

 tral New- York, become less and less conspicuous in a westerly direction. 



*Report on the Geology of Wisconsin, p. 67. 1861. 



tl am inclined to believe that I have overestimated the thickness of the limestone 

 at Leclaire from the presence of lines of false bedding, but I have had no opportu- 

 nity of a re-examination of the locality. 



