44 LOWER PENINSULA. 



particularly Stromatopora Wortheni, Favosites Hamiltonensis, 

 Cyathophyllum profundum, Strombodes Alpcnensis, Chonophyllum 

 ponderosum, many Bryozoa and various Brachiopods of the usual 

 Hamilton species, etc. The rock makes an excellent white, quick- 

 slaking lime. Similar strata of less brecciated structure, and inter- 

 laminated with soft, soap-like, whitish green clay are uncovered in 

 the race of Mr. Broadwell's saw mill on Thunder Bay River. The 

 clay incloses a profusion of splendidly preserved Bryozoa and corals, 

 also some Crinoids (Dolatocrinus) and Brachiopods. The exact rela- 

 tive position of the strata exposed in this locality I was unable to 

 ascertain. A bubble-like upheaval of the beds has its centre in 

 the river bottom and by the dam thrown across the river — the most 

 instructive portions of the section are thus set under water. Only a 

 short distance up the river, on the side of the road leading to Trow- 

 bridge's mills, a small knob is formed by the same light-colored, 

 smooth fracturing, brecciated limestones, which there seem to re- 

 pose in undisturbed original position on blue calcareous shales, 

 with seams of silico-argillaceous limestone. The river, which 

 passes only about loo steps from the hillock, has cut its bed 

 through these subjacent shales to a depth of 50 feet, and 

 for a whole mile the ledges are exposed in high bluffs. The 

 shales inclose a great variety of well-preserved fossils : Atrypa 

 reticularis, Spirigera concentrica, Cyrtina Hamiltonensis, Cyrtina 

 umbonata, Spirifer mucronatus, Spirifer divaricatus, Spirifer granu- 

 liferous, Spirifer fimbriatus, Terebratula Linklseni, Strophodonta 

 demissa, Pentamerus papilionensis, Crania crenistria. Crania Ham- 

 iltonise, and numerous Bryozoa, Phacops bufo, etc. A few inter- 

 stratified seams of a silicious limestone are a conglomerated mass 

 of silicified shells of Cyrtina umbonata and of a few specimens 

 of Spirigera concentrica. 



The argillaceous limestones interstratified with the shales 

 were a number of years ago used for the fabrication of hy- 

 draulic cement. Expensive kilns stand abandoned at the foot of 

 the river bluffs. Mr. Trowbridge, their former owner, informs 

 me that sometimes an article of very good quality was pro- 

 duced, but the success was so uncertain that the cement never 

 came into reputation in the market, and after a short time he 

 gave up the undertaking. Whether the failure to make a uniform 

 product was in the use of different beds, some of which would not 



