354 \. W. GRABAU — SILURO-DEVONIC contact IX NEW YORK 



The sandstone rests on u " hard, compact dolomite rock, mottled with 

 light and dark bine cloudy specks, resembling castile soap." These 

 strata, referred to the Lower Helderberg by Rominger, are frequently, 

 though not always, brecciated, with fragments of various ledges inter- 

 mingled and recemented. The brecciated condition is traceable through- 

 out a great portion of the Peninsula, is very prominent on the island of 

 Mackinac, where the concretionary and conglomeritic phases also occur, 

 and is noted again at Goderich, in Canada. 



Often "a regular unbroken seam of limestone alternates with the 

 brecciated layers."* The lower non-brecciated beds are of the same 

 lithologic character as the fragments composing the breccia. 



The fossils obtained from these beds include, according to Rominger: 



Meristella hevis (Vanuxem). Spirorbis. 



Leptoccelia (CaJospini) concava Hall. Cyrtoceras. 



Hetzia (Rhynchospira) globosa Hall. Vegetable remains. 

 Megambonia (Pterinea) aviculoidea Hall. 



In Wisconsin, according to Chamberlin (1877), rocks probably of 

 this age rest on Niagara limestone, and are but sparingly developed. 

 They are overlaid by limestones of the Hamilton group, which, in the 

 absence of intervening beds, rest directly on the Niagara. The great- 

 est thickness recorded for the so-called " Lower Helderberg " rocks of 

 Wisconsin is 7 feet 21 inches. This is in Fredonia, Ozaukee county, 

 in the bed of Milwaukee river. It is a dolomitic rock, in several layers, 

 some of which are full of Leperditia alia. The following species were 

 described from this rock by Whitfield (L 882) : 



Orthis subcarinata Hall. Pterinea aviculoidea Hall. 



Orthis oblata Hall. Leperditia alia (Conrad). 



Meristella ( Whitfieldella)nucleolata (Hall). 



The reference of the various Meristoid brachiopods from the western 

 Manlius limestone to Lower Helderberg species of Meristella is open to 

 question. It is much more likely that they all belong to Whitfieldella. 

 To the same genus Whitfield's Nucleospira rotundata is probably to be 

 referred. The occurrence of W. nucleolata in the Wisconsin Manlius is 

 of interest, this species being otherwise known only from the Coralline 

 limestone of Schoharie county, New York. The great similarities of the 

 faunas of this limestone from Ohio, from Michigan, and from Wisconsin 

 is noticeable, and its close relation to the fauna of the Erie county Man- 

 lius limestone is also evident. 



* Rominger, 1896, p. ;5:i. 



