of the Water at the United Mines. - 105 



witnessing the fact just named in the deep mines in the 

 Gwennap district, and in almost every case the lodes at the 

 lowest points are composed of hard compact quartz, almost 

 free from the presence of minerals, and yet the water issuing 

 from those parts is of the highest temperature, which cer- 

 tainly strengthens the opinion that the source of heat is from 

 a still greater depth ; and its effects not being so evident in 

 those places may be accounted for by the absence of those 

 substances in the lodes on which the action of heat would 

 manifest itself. But whilst it is admitted that the tempera- 

 ture increases with the depth, it should be observed, that it 

 is not found to be the same at the same depth, even in parts 

 of the same mine which are only a few fathoms' distance from 

 each other. In different mines in the same locality, and in 

 precisely similar formations, the result is often very differ- 

 ent. As instances of this, I will refer to the Consolidated 

 Mines, which adjoin the United Mines, and the lodes in each 

 bear the same direction, and run parallel to each other. The 

 former have been worked to the depth of 316 fathoms from 

 the surface, whereas the latter have only been worked 260 

 fathoms, or 56 fathoms less than the first. The highest tem- 

 perature in the Consolidated Mines has been 98° Fahrenheit, 

 whilst in the United Mines it is 106°. Again at Tresavean, 

 the depth of which is 320 fathoms from the surface, the high- 

 est temperature yet observed is about 95°. It should, how- 

 ever, be noticed, that the deepest part of Tresavean is in 

 granite formation, and that the Consolidated and United 

 Mines are in slate. 



These circumstances go to shew that there must be other 

 causes producing heat, apart from the mere depth of the 

 mines ; and, without being prepared with conclusive evidence 

 as to its origin, or the source from whence it proceeds, 1 can- 

 not help remarking that the degree of heat is very much in- 

 creased by its passing through immense bodies of mineralized 

 matter powerfully acted on by galvanic agency. 



I feel that I have now carried these hasty remarks as ftir 

 as it is safe to go, without entering upon ground which it 

 would be dangerous for me to venture on ; and I will bring 

 them to a close, by expressing a hope that they may serve. 



