HAMILTON GROUP. 5 1 



bluff from the east shore of the island, and where, when the lake is 

 quiet, a huge stairway, formed by large rock tables, divided by 

 vertical fissures into rhomboids, can be observed, leading down, step 

 by step, into greater depths, until finally lost to view. Presque 

 Isle Lighthouse Point is composed of the same strata, and inter- 

 mediate between the lighthouse and False Presque Isle, on several 

 parts of the shore, they come to the surface, the rest of the shore- 

 line being a sand or gravel beach. 



Significant of these strata are two fossils, which I found in every 

 one of the outcrops observed. One is Lucina elliptica, the other a 

 species of Euomphalus, closely related, or perhaps identical with 

 Euomphalus Dekewyi of Billings. Associated with these fossils in 

 the outcrops of Presque Isle are, Stromatopora textilis, Stromato- 

 pora Wortheni, Diphyphyllum rectiseptatum, Favosites (rare), Spi- 

 rigera concentrica (small, globose form), Spirifer gregarius, Atrypa 

 reticularis, and Pentamerus. On Middle Island, I found, in addition 

 to the first, Cystiphyllum, Atrypa reticularis with very fine ribs, a new 

 species of Pentamerus (P. nucleolus), a Strophodonta, two species 

 of Bellerophon, a Pleurotomaria, and several other Gasteropods, a 

 large Myalina (M. carinata), Avicula flabella, and casts of other 

 bivalves, Orthoceras, and a Nautilus with quadrangular oblong dia- 

 gram of volutions. The scarcity of Favosites and Cyathophyllum 

 in the strata of all the localities under consideration is peculiar ; in 

 all the rock beds, above and below, these two genera are the 

 predominating types. The rock ledges composing Middle Island 

 are best exposed on the north side of the island ; the ledges are 

 uneven-bedded, not thick, a dark gray-colored, somewhat brittle 

 limestone ; some beds are mottled with porous, lighter-colored 

 dots, and sparingly intermingled^ with flint concretions. The 

 whole thickness of the exposed beds 'successively coming to the 

 surface is not over 20 feet. The exposures at Presque Isle Light- 

 house Point exhibit at the water's edge limestones entirely similar 

 to those of Middle Island ; higher beds denuded during the ex- 

 cavation of the foundation for the lighthouse are an easy weather 

 ing limestone with an abundance of cherty concretions. 



At Crawford's quarry the shore-belt rises in two terraces, partly 

 covered by drift, partly presenting rock exposures. At the water's 

 edge, rock bluffs projecting to a height of from 10 to 15 feet are 

 composed of drab-colored limestones mottled with darker, more 



