674 GEOLOGY OF OHIO. 



terminated in its being assigned, without dissent, to the Niagara series. 

 It forms the crowning member of this series in the northern and western 

 portions of its widely extended field. It has received the names of vari- 

 ous localities where it is distinctly shown, being styled the Guelph forma- 

 tion in Canada, the Racine beds, or Milwaukee beds, in Wisconsin, and 

 the Bridgeport beds in northern Illinois. In southern Ohio no local 

 name can be selected so appropriate and free from ambiguity as the 

 Cedarville limestone, constituting, as it does, the only member of the 

 Niagara series shown in the extensive quarries opened at this village. 

 There is not, however, as great a thickness of the limestone shown at 

 Cedarville as at Yellow Springs. The exposure of the Niagara rocks at 

 this last named place has been repeatedly referred to, and now, since all 

 the elements that enter into it have been given, a somewhat more 

 detailed account will be supplied. It is decidely the best section of the 

 Niagara series shown in Greene county, and is but little inferior to the 

 section at Holcomb's lime-kilns, below Springfield. 



The Clinton limestone follows up the Yellow Springs Branch to a point 

 nearly opposite the extensive quarries of W. Sroufe, Esq. Starting from 

 this well-settled base, eighty -four feet of the Niagara rocks are traversed 

 in a very steep ascent. The uppermost thirty feet are shown in the 

 quarries before referred to ; the lowermost thirty feet are well shown in 

 the adjacent banks of the Cascade Branch. Exposures of the intervening 

 beds are not wanting in the immediate vicinity. The thickness here 

 given is thus divided : 



Cedarville beds 22 feet. 



Springfield stone 24 " 



West Union cliff 8 " 



Niagara shales 30 " 



Total 84 " 



The twenty-two feet of the upper division are further re-enforced in the 

 higher ground adjoining the ravine. It gains ten feet, at least, in the 

 land immediately to the westward, and may be safely taken as not far 

 below forty feet in its total thickness here. 



The identification of this stratum has been made complete by the dis- 

 covery of a considerable number of fossils in it that are peculiar to the 

 above named horizon. A list of a dozen or more of these forms common 

 to the Guelph and the Cedarville beds is given in the reports of Highland 

 and Clarke counties. Of these the most prominent and characteristic 

 are two great shells, the enormous and somewhat abnormal brachiopod 

 Trimerella, and a lamellibranch shell of even greater bulk, Megalomus 

 Canadensis. Trimerella is represented in these beds not only by the 



