HAMILTON GROUP. 49 



Strophodonta erratica, Strophod. demissa, Productella dumosa, a 

 large Myalina Euomphalus, etc. 



A few miles east of Long Lake we find the shore of Lake 

 Huron lined with exposures of the black, shaly limestones', 

 agreeing with the strata on top of the hills near the former, 

 everywhere containing an abundance of Stromatopora Favo- 

 sites, Cyathophyllum profundum, as the prevailing fossil forms, 

 besides other species common only in certain localities ; as, for 

 instance, a species of Zaphrentis, which I found in great quan- 

 tities at Section 34, in Township 32, Range 9, east, but which, in 

 all other localities north and south from there, was rare or miss- 

 ing. I also found Favosites digitatus more common there than 

 elsewhere. On Thunder Bay Island, the variety of fossils in the 

 black limestone strata is greater than I found it in any other 

 place. Besides the above-mentioned leading forms of Stromato- 

 pora and of corals, the strata are rich in Bryozoa and in Brachio- 

 pods. Among the latter, I may mention Atrypa reticularis, Spiri- 

 gera concentrica, Spirifer zigzag, Spirifer mucronatus, Terebratula 

 Linklaeni, Strophodonta erratica, and Pentamerus aratus. Ortho- 

 ceras, Gomphoceras, Proetus crassimarginatus, and Phacops bufo 

 also belong to the more common fossils of the island. Sugar 

 Island represents the same strata, but the rock beds there are 

 mostly covered by drift. Little Thunder Bay is a deep recess in the 

 coast, situated in Township 31, R. 9, Section J^. Its entrance 

 is very shallow, not always deep enough to admit a Mackinaw 

 boat. The head of the recess is formed by a large sink-hole, 

 which in the middle has a depth of 100 feet. A semicircle of 

 rocky bluffs of from 25 to 30 feet elevation surrounds this deep 

 pot-hole. The external portion of the semicircle is forjned by the 

 edges of horizontal rock beds projecting in vertical walls ; a belt in 

 front of them is composed of loose masses of the same rock, broken 

 off and dipping in rapid inclination or in irregular, uptilted posi- 

 tion toward the margin of the water-basin. The strata are the 

 same as on Thunder Bay Island, but of lighter color, and more 

 interlaminated with soft, shaly seams. 



One township further north, in T. 32,, R. 9, Sect. 6, directly west 

 of Middle Island, on the side of a small creek flowing southeast- 

 ward into Lake Huron, a chain of vertical rock bluffs, about 

 16 feet in height, is found commencing about half a mile from 

 4 



