HAMILTON GROUP. 6 1 



formation, the equivalent of the Genesee shales of New York, is de- 

 posited. 



In the drift composing the lake terraces on the south shore of 

 Little Traverse Bay, large numbers of slabs of a tough black shale 

 are intermingled. The shale is easily ignited, burning with a 

 bright flame, and is by many persons taken for coal, or as an 

 indication of the existence of coal in that district. The shale 

 contains a great abundance of well-preserved fossils of the Hamil- 

 ton group, in calcified condition ; fan-like expansions of Fenestella, 

 Polypora, each genus represented by various species, Stictopora, 

 Fistulipora, and other Bryozoa are in great perfection ; several forms 

 of Stromatopora, incrusting other fossils, or in laminar expan- 

 sions, Cyathophyllum Houghtoni, Cyathophyllum profundum, Cys- 

 tiphyllum Americanum, Favosites Hamiltonensis, Favosites digita 

 tus, Aulopora, Syringopora, Tentaculites, Conocardium, Atrypa 

 reticularis, Spirigera concentrica, Pentamerus papilionensis, Tere- 

 bratula Linklseni, Strophodonta erratica, Strophodonta nacrea, 

 Phacops bufo, and Proetus crassimarginatus have been noticed. 



During the description of the Hamilton series of Little Traverse 

 Bay, several seams of similar black shales interlaminated with the 

 other strata have been pointed out, but in none of the outcrops 

 were more than a few inches of such shale beds noticed, while the 

 slabs found in the drift seem to have been parts of thick ledges. 

 It is most likely the lower seam of the two, exposed below the 

 horizon of the blue fossiliferous shales (acervularia shales), from 

 which the drift specimens originate. 



The thickness of the rock series of the Hamilton group exposed 

 along the shore of Little Traverse Bay is not accurately determina- 

 ble. No continued sections through more than 50 feet of strata 

 are seen in one place, and the rock character of beds in their hori- 

 zontal extension is subject to so many variations, that no sure 

 conclusion on the identity of rock ledges in distant outcrops can 

 be based on it. The palaeontological features of the strata are also 

 not strongly marked. Although certain forms of fossils are gene- 

 rally associated in certain layers, the majority of fossils charac- 

 teristic of the Hamilton group are so equally distributed through- 

 out its whole thickness, that all of them can be found in almost 

 any position at the base or in the upper horizons. There are layers 

 filled with the same species of Stromatopora found in repeated 



