﻿128 H. A. Wheeler — Temperature Observations. 



The Quincy mine is less than a mile from Portage Lake ; in 

 fact some of the workings on the vein extend nearly to the 

 lake-side, while the melaphyre belt that the mine works crosses 

 the lake. The mine workings, though now very much below 

 the bottom of the lake, are quite free from water, the little 

 they have being mostly of surface origin. 



It is to this fact of the proximity of the mines to the cold 

 waters of Lake Superior, that I wish to draw the reader's atten- 

 tion. For so far as I have been able to gather similar data, I 

 have not found another instance where such very low thermic 

 gradients have been observed, with the single exception of the 

 Dukinfield Coal Pit, near Manchester, England, where a gradi- 

 ent of 90 feet to the degree is recorded. As no details were 

 given with this, it is impossible to say whether this is the nor- 

 mal gradient for that region, or whether modifying influences, 

 like an excessive influx of water, or other causes, may have 

 made this simply a local rate. While the average rate of these 

 copper mines is most exceptionally low and noteworthy, having 

 quite possibly the lowest thermic gradient on record, the varia- 

 tions among the different mines is quite striking. In account- 

 ing for it, it should be stated that there is no reason to suspect 

 that the observations of any one mine (with the exception of 

 the Tamarack) are any less trustworthy than another. Nor 

 does the nature of the rock in which the mine is worked seem 

 to offer an explanation, for while three quite different classes 

 of "lodes" are presented, the greatest variations occur in those' 

 whose characters are identical, to wit : the Atlantic, Osceola 

 and Quincy, which are all in melaphyre. Though each of these 

 mines is on a different belt of melaphyre, the general char- 

 acter of the entire formation is quite similar and alike, or a 

 series of conformable, parallel belts of alternating conglomer- 

 ates, melaphyres and diabase. The mines are quite similar in 

 respect to freedom from water, all being comparatively dry 

 mines, considering their extensive character, and what little 

 water they have to contend with is quite generally of surface 

 origin. In the mines mentioned there is at present no evi- 

 dence of active chemical changes or reactions observable to 

 cause this differentiation, while the general system of mining 

 with rock-drills is carried on in all of them. 



But when we consider their relation to one another as re- 

 gards their proximity to Lake Superior, we are at once im- 

 pressed by the close relationship between this distance and the 

 thermic gradient ; the mines nearest to the lake shore have the 

 lowest gradient, while those farthest away have the higher or 

 more rapid rate. "When we consider the magnitude of Lake 

 Superior and remember that only its surface waters change in 

 temperature, as the great body of its deep waters remain con- 



