HAMILTON GROUP. 



45 



answer, or in the management of the burning process, I can not 

 tell. 



From Trowbridge's mills, higher up the river, the strata are hid- 

 den from view for several miles ; they appear again under the bridge 

 crossing the north branch of Thunder Bay River. Judging from the 

 rock character and the fossils, the strata belong to about the same 

 horizon as those near Trowbridge's mills. 



In Township 32, R. 6, east, Section 34, on the farm of Mr. 

 Marston, close to his dwelling-house, a large funnel-shaped sink- 

 hole without an outlet attracts attention. It occupies the area 

 of a few acres, and has a depth of about 25 feet; a strong spring 

 issues from the side of the depression and disappears again in its 

 bottom in the crevices of the rock. 



The bottom strata, seen in a thickness of about 8 feet, are 

 hard, bituminous limestones, with delicate laminar striation in the 

 direction of the bedding and fissible into thin flags. Near the 

 upper terminus of the rock strata a seam about one foot in thick- 

 ness of a cellulose, brecciated quartz rock, mottled with various 

 red, brown, or yellowish colors, and* containing distinct casts of fos- 

 sils, is intercalated. Above it follows a coarsely crystalline, tough, 

 brownish-gray dolomite, which contains large Euomphalus-like 

 coiled shells, Cystiphyllum, and indistinct specimens of Stromato- 

 pora ; its thickness is from 8 to 10 feet. Next above is a sili- 

 cious limestone full of silicified specimens of Stromatopora Wor- 

 theni, Favosites digitatus, Syringopora nobilis, Spirigera concen- 

 trica, and the same large coiled shell as in the dolomites below ; its 

 thickness is 4 or 5 feet, and over the top a few layers of com- 

 pact, light-colored limestones are spread. About a mile from 

 Marston's the road passes not far from the river, where it inter- 

 sects the southwest corner of Section 34 in the same town. It 

 flows there in a long series of rapids, over hard, bluish, crystalline 

 limestones containing shell fragments and Crinoid joints. The 

 banks of the river, about 18 or 20 feet high, are all formed 

 of drift, and the relative position of these rock beds can not 

 be made out. On Section 28 of the same township, on Mr. 

 Johnson's farm, in a well 21 feet deep, blue-colored argilla- 

 ceous limestones and intermediate shale beds were penetrated ; of 

 fossils, I noticed in them Atrypa reticularis, Spirifer fimbriatus, 

 Spirifer granuliferous, and Crinoid stems ; one of the layers was a 



