HAMILTON GROUP. 63 



the palaeontological features of certain horizons in the group are 

 not well enough marked to enable us to make such identifica- 

 tion. The fauna of the Hamilton area remained uniformly the same 

 from the beginning to its end, as I have intimated once before 

 in a previous page. We find differences in the association of fos- 

 sils in various beds, but these are rather induced by local condi- 

 tions favoring the development of certain forms and uncongenial 

 to others, than by a change in the character of the fauna, whose 

 standard representatives always make their appearance again, if 

 they have been missing for a while in some of the layers. 



My estimate of the thickness of the Hamilton series in Thunder 

 Bay region, about 600 feet, is based on the results of the artesian 

 borings heretofore given, which I will briefly recapitulate. I 

 stated that the strata of Partridge Point and the next lower 

 Stromatopora beds of Stony Point, with the intercalated fossil- 

 iferous shale beds, amount in the aggregate to at least one hun- 

 dred feet, and that their superposition on the beds in which the arte- 

 sian boring begins is directly observable. The drilling went first 

 through 400 feet of limestone strata of not accurately specialized 

 character in the records kept of the boring, and below them, 

 through a shale bed of 80 feet in thickness, containing a great variety 

 of characteristic Hamilton fossils, proving positively a thickness of 

 580 feet for the Hamilton series at this spot. This shale deposit 

 I suppose to be identical with the blue shales penetrated to a 

 depth of 50 feet under the limestone bluffs in Town. 32, R. 9, Sect. 6, 

 by the exploring shaft of the attempted marble quarry. The rock 

 series composing Middle Island, Presque Isle, and other localities, 

 underlies the blue shales, and is in this report considered a part of 

 the Hamilton group, and is not overestimated by allowing for it 

 a thickness of 60 or 70 feet, which would give to the Hamilton 

 series of Thunder Bay region a total thickness of 650 feet. 

 According to the boring record, nearly 500 feet of lower strata in 

 the drill-hole, down to the salt-rock deposits of the Onondaga 

 group, should be claimed as representatives of the Helderberg 

 group. 



