HAMILTON GROUP. 



41 



only be small, proportionate to the surface of salt rock exposed to 

 the solvent, was pumped out, it was to be expected that only a 

 weak brine could be obtained. But this would have soon reme- 

 died itself ; by constant pumping a larger cavity would have been 

 formed, and the surface offered to the water for solution would 

 constantly have increased, so that a reservoir would finally be 

 formed capable of furnishing a supply of strong brine which 

 could no longer be exhausted by the pumps. Whether any use 

 was made of these hints, I do not know, but the fact is that this 

 very valuable discovery has lain idle for several years, which is 

 much to be regretted, as I have not the least doubt that, by a 

 little patient application of the pumps, it would soon yield a con- 

 stant supply of strong brine. The highest beds of the Hamilton 

 series at Thunder Bay are seen at Partridge Point, on the south 

 side of which, in Squaw Bay, the bituminous black shales of Ohio 

 directly overlie them. Sulphur Island, in front of Squaw Bay, is 

 also covered by the black-shale formation. 



The top layers on Partridge Point are thin-bedded, hard lime- 

 stone slabs, seen in the thickness of a few feet ; they contain no 

 fossils. Next below them follow calcareo-arenaceous shales of 

 bluish or greenish color, alternating with seams of limestone, which 

 face the lake in a bluff along the north side of the point, pro- 

 jecting about 12 or 15 feet above the water level. The shales 

 and limestone beds are crowded with fossils in a good state of 

 preservation. A great variety of Bryozoa, particularly of the ge- 

 nera Fenestella, Polypora, Hemitrypa, Stictopora, Fistulipora, and 

 Trematopora, belong to the most abundant forms, besides corals, 

 Cystiphyllum Americanum, Cyathophyllum geniculatum, Cyathoph. 

 Hallii, Diphyphyllum Archiaci, and various forms of Favosites, 

 Syringopora, Aulopora, Dendropora. Crinoids are very well repre- 

 sented by the genera Megistocrinus, Dolatocrinus, Nucleocrinus, 

 Pentremites, Lepadocrinus. Of Brachiopods occur : Atrypa reti- 

 cularis, Spirifer granuliferus, Spirigera concentrica, Cyrtina Ham- 

 iltonensis, Terebratula romingeri, etc. ; of Trilobites, Phacops bufo 

 and a species of Proetus. In front of these bluffs, at a distance of 

 about one mile, are two islands, Bear Island and Grass Island, on 

 which I expected to see the next lower beds exposed, but all their 

 surface is composed of boulder drift. 



Likewise on the main shore, the rock strata below the shales of 



