HELDERBERG GROUP. y^ 



of successive ledges become exposed. The breccia is formed of 

 angular rock fragments ; sometimes larger masses, composed of 

 several consecutive layers, retaining their regular stratified posi- 

 tion to each other, lie inclosed in it, often also a regular, unbroken 

 seam of limestone alternates with the brecciated layers. 



The principal part of the ledges resembles in all particulars the 

 rock of the Newport quarries ; the same fossils are found in them, 

 only in greater abundance and variety. Meristella laevis, Lepto- 

 coelia concava, Megambonia aviculoidea, casts of several forms of 

 bivalves and gasteropods, and a small spirorbis-like shell, are the 

 usual forms met with, besides a profusion of the above-mentioned 

 vegetable remains [pervading the rock beds. Druses of coelestine 

 and calcspar, and veins of these minerals, filling the fissures of 

 the rock, are very abundant. 



Eurypterus remipes and Leperditia alta, the two typical forms 

 of this horizon, I could not find in this locality, but on Put-in- 

 Bay Island both fossils are found in association with the others 

 above mentioned, and in beds which, by their lithological charac- 

 ters, leave no doubt of the identity of the strata in both places. 

 Of the emailled corpuscles with serrate edges, which I found in 

 the dolomite of Flat Rock, and suggested might be the remains of 

 fishes or crustaceans, I found several at Point-aux-Paux. South 

 of Point-aux-Paux, toward Monroe, we find the same rock beds 

 everywhere close under the surface, with only a few feet of drift 

 on them. The quarries alongside of Raisin River, up to Dundee, 

 are all opened in beds of this horizon. In the quarries of Plum 

 Creek, a short distance south of Monroe, by the undulations in 

 which the strata rise and sink, about twenty feet of rock 

 beds come to an exposure. Uppermost are fine-grained, light- 

 colored dolomitic limestones in beds a few inches thick, and 

 in the aggregate reaching six feet. Next below is a compact 

 stratum of oolith from eighteen inches to two feet in thick- 

 ness, which makes a good building material. Lower are thin, 

 rugose ledges of limestone with intervening narrow seams of a 

 black shale mass ; these are succeeded by about two feet of a gray 

 and blue mottled dolomite rock, after which are again thinly 

 laminated limestone slabs with intermediate black shale seams. 

 The surface of these limestone slabs is covered by ramified relief 

 forms, apparently of vegetable origin. The lowest beds in the 

 3 



