314: GEOLOGY OF EASTERN WISCONSIN. 



quadrata, Leptsena canierata, Streptorhynchus filitextus, Murchisonia major, Bucania 

 expansa, Trochonema umbilicata, Maclurea (large casts, three inches in diameter), Con- 

 ularia Trentonensis, Dictyonema (a species with veiy delicately reticulated fronds ex- 

 panding from a transversely-wrinkled hollow cylindrical stem, with a shining carbon- 

 aceous surface) ; also indistinct specimens of Chsetetes frondosus and Crinoid stems are 

 included in the rock," p. 57; to which may be added a new species of Stictopora, Ra- 

 phistorna lenticularis, a Murchisonia allied to M. gracilis, but larger, a Pleurotomaria, 

 and an Orthoceras. 



In the way of recapitulation, it may be observed that a comparison 

 of the fossils that have now been enumerated, in connection with the 

 several localities, shows, (1) that there are a considerable number that 

 range throughout the whole Trenton period, including the Cincinnati 

 epoch, and are, therefore, of no service in discriminating between its 

 subdivisions; (2) that there is another portion whose occurrence is 

 chiefly confined to the strata below; and (3) that there are a few that 

 are not authentically known to occur either above, or below, the horizon 

 under consideration, and may be regarded as characteristic of it. Of 

 this latter number, Receptaculites Oweni and Murchisonia bellicincta, 

 or major, are the most constant and reliable. Lingula quadrata, al- 

 though rare in other beds in this region, does not appear to be strictly 

 confined to this subdivision. Fusispira ventricosa, F. elongata, and 

 an intermediate form, are, perhaps, to be added to the list, as they range 

 from Walworth to Oconto county, and are not found in the collec- 

 tions of the survey in any other stratum. 



It will be seen that the change in the nature of the rock com- 

 menced in Dodge county, and was essentially completed in Winnebago 

 county, being gradual and progressive through -iO or 50 miles; and 

 that it consisted mainly of the addition of shaly or argillaceous mate- 

 rial; and that the increase in the variety and number of the fossils ac- 

 companied the increase of the clayey ingredient. 



By a comparison with the formations already described, and those 

 remaining to be treated, it will further be seen, that they also undergo 

 some modification at essentially the same latitude, the cause of which 

 can be better understood when all the facts are before us. 



THE CINCINNATI SHALES AND LIMESTONES. 



The Galena limestone is succeeded by a series of shales and lime- 

 stones, constituting what will be known in this report as the Cincin- 

 nati group, a name now quite generally adopted for this geological 

 horizon, although there is still some difference of opinion as to the 

 lower limits which should be assigned to the application of the term. 

 It here includes all the beds known to lie between the upper surface 



