HAMILTON GROUP. 39 



ron, to the shores of Canada and Wisconsin, has previously been 

 mentioned. North of the indicated line, all of the surface of the 

 peninsula is formed by the Hamilton strata, excepting the small 

 strip of shore at McGulpin's Point, which is described as composed 

 of the upper Helderberg limestones. The Hamilton group in 

 New York is pre-eminently a shale formation, with subordinate 

 beds of limestone ; in Michigan it has more the character of a 

 limestone formation with but a subordinate development of 

 shale beds. 



Natural sections of large extent, by which the thickness of the 

 formation can be estimated, do not exist ; by borings made in 

 Alpena, its thickness is found to be much greater than formerly 

 had been supposed. One of the borings was made more than 

 ten years ago, but no accurate record was kept of it. At that 

 time a bed of rock salt was struck in the bottom of the well, 

 and I myself saw more than a bushel of salt in yellowish crys- 

 tals which was brought up by the sand pumps ; still no further 

 use was made of this discovery, and it is only within the last 

 few years that the strong stream of mineral water discharged 

 from the bore-hole has received attention and been used for its 

 strong medicinal properties. At present it is led by tubings to a 

 bathing institution close to the landing-place at the bay. The 

 mineral water is strongly impregnated with hydrosulphuretted gas. 

 It flows from a higher level than the bottom of the well, but 

 has a considerable proportion of chloride of sodium in solution, 

 which probably rises from the lower part of the bore and mingles 

 with the upper sulphurous water. An analysis made by Dr. Duffield 

 gave 237 grains of solid matter to a gallon of the water, as 

 follows : ■; 



Bicarbonate of soda 15-736 grains. 



" "■ lime 55-136 " 



" " magnesia 62.920 " 



" iron 1.840 " 



Sulphate of lime , . , . . 30.056 " 



Chloride of sodium 68.256 " 



Silica and alumina 3.088 " 



Organic matter 0.928 " 



Sulphuretted hydrogen 3.91 cubic inches per gallon. 



