54 LOWER PENINSULA. 



and the hilltops are composed of drift, but the lower levels along 

 the shore arc formed by an almost uninterrupted string of rock ex- 

 posures, from the head of the bay clear round to Big Traverse Bay, 

 where the last beds of the Hamilton group dip under the black 

 shale at the village of Norwood, in the south corner of Town. 32, 

 Range 9, west. The Hamilton group, as developed on the west 

 shore, is chiefly a limestone formation, but its rock character differs 

 in many respects from the Thunder Bay series. The first outcrops 

 at the head of the bay are found about a mile and a half east from 

 the mouth of Bear Creek, which enters the bay at the foot of 

 the newly built village of Petosky, the present terminus of the 

 Lansing and Saginaw Railroad. Below the railroad depot, vertical 

 rock bluffs of 45 feet elevation face the bay ; eastward the bluffs 

 become lower, and finally disappear altogether, giving place to a 

 sand and gravel beach which lines the east end of the bay. 



The lowest strata of these bluffs are seen on its eastern end, a 

 blue, argillaceous, hard lime rock cropping out at a level with the 

 water-line. The higher beds have almost the same lithological 

 character, being light drab-colored, porous dolomites, with a dull, 

 earthy fracture. The lower strata are very even-bedded, of finely 

 laminated structure ; they contain numerous band-like, compressed, 

 carbonaceous, vegetable stems, similar to Psilophyton, and bones of 

 fishes ; the casts of small ' bivalve shells, or branching forms of 

 Favosites also cover the surface of some ledges, but generally fossils 

 are rare in these lower beds. The upper strata forming the verti- 

 cal part of the bluffs are not always so regularly stratified ; by 

 weathering, the seams of the bedding become obliterated on 

 the surface of the exposed walls, which sometimes appear to 

 be one solid mass. By digging into them, however, the stratifica- 

 tion becomes clearly observable. Some parts of the rock are 

 mottled with darker, more compact blotches than the rest of the 

 substance, which in a dry state rapidly absorb water. These 

 blotches seem to be portions of the rock unaltered from their origi- 

 nal condition, while the lighter-colored surrounding mass has been 

 leached out by percolating waters, which dissolved the sparry 

 calcareous cement, whereby the fine crystals of the less soluble 

 dolomite spar were held together, leaving the latter a soft, porous 

 skeleton. 



Fossils are very abundant in these upper layers, but are not 



