710 a. c. lane geotherms of lake superior copper country 



Lake Superior not Efficient 



In his work in 1886, the first that brought into relief the low gradient 

 of the copper mines of Michigan as compared, for instance, with those 

 in Montana (the North Butte Mine at Butte, Montana, has at 2,800 feet 

 a rock temperature of 107 degrees Fahrenheit), Wheeler suggested that 

 the low gradient might be due to the cooling effect of Lake Superior. 



Unfortunately, this suggestion was taken up by Koenigsberger, the 

 great European and world writer on this subject, in his paper before the 

 International Mexican Congress/ When he speaks of a "small'^ gradient, 

 he means thereby one in which are few feet needed to obtain 1 degree 

 rise, 9 degrees Fahrenheit = 5 degrees centigrade, 1 degree Fahrenheit 

 for n feet = 1 degree centigrade for 0.55 meters. Thus no change in 

 temperature at all would be a "large" gTadient ! He says (page 12) that 

 the geothermal gradient is "greatest" near the surface, which agrees with 

 what should be the case if the mean surface temperature has risen since 

 the Ice Age. On the other hand, "the more recent the eruption, the 

 smaller the geothermic gradient." This is altogether in harmony with 

 the contrast between the temperature of the copper mines of Butte, Mon- 

 tana, where the igneous activity is Mesozoic, and those here cited, where 

 the igneous activity is probably before the Taconic uplift and pre-Ordo- 

 vician. Thus Wheeler^s suggestion is spread through the literature. It 

 can not be too strongly emphasized that Lake Superior has nothing to 

 do with the gradient. 



In the first place, it will be noticed from the table above that the mean 

 annual temperature of Calumet is only a degree or so from that of the 

 bottom of Lake Superior, which is that of the maximum density of water 

 (38.8 degrees Fahrenheit), a mere trifle compared with the differences 

 in temperature that would exist had Michigan the same gradient as 

 Montana. 



In the second place, Lake Superior is 5 miles away, and the lateral 

 effect of cooling on a point only one mile down, common sense would 

 indicate could be but slight, even if B. 0. Peirce had not figured it out 

 with a thorough use of mathematics in volumes 34 to 38 of the Proceed- 

 ings of the American Academy of Sciences,^ 



In the third place, the gradient in the Freda well, down on the edge 

 of Lake Superior, is higher than in the deep mines back from the shore. 



■^ Also Transactions Institution of Mining Engineers, vol. xxxix, part 4, New Castle- 

 upon-Tyne, England, p. 11 of excerpt. 



« Vol. 34, pp. 22-25 ; see also vol. 36, pp. 1-16 ; vol. 38, pp. 651-660, or Williamson 

 and Adams, Physical Review, n. s.. vol. xiv. 1919. pp. 101, 103. 



