1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



lodes, and these are not so warm as the rocks. Now the cross veins 

 appear to carry downward the largest quantity of rain-water. Tin- 

 veins are colder than copper- veins. Granite is very sensibly colder 

 than slate : at 240 fathoms, one is recorded 76*15°, the other 89-4°. 

 From the surface to 150 fathoms the rise of temperature seems to 

 follow a ratio diminishing downwards, hut from that point it aug- 

 ments again. 



The latest experiments by Mr. Pox bring out the same variations 

 in regard to the rocks and lodes, and the influence of water-streams 

 on the observed temperature. His experiments were made in the 

 sohd. They show six cases in granite, which give a ratio of 54, 

 63-7, 48-4, 71, 55-3, 52-1, mean l°in 57*4 feet, and five in killas, 32, 

 39, 36-7, 41-3, 43-7, mean 1° in 38-5 feet*. If waste of heat depend- 

 ing on soil may be thought to be constant, isothermals under these 

 rocks would be suddenly bent upwards in the killas, the flexure being 

 greatest in the greatest depths. 



IS^ow, as granite is the better conductor for heat, it would seem 

 that here we may recognize the fact that conduction retains a sensible 

 share of communicating heat upwards, thus confirming the view that 

 this heat augments regularly downwards to a considerable depth. 



The highest temperature recorded in the Cornish mines is 116° 

 (the temperature of the hot spring at Bath). It occui's in a warm 

 spring in United Mines at 2bK> fathoms, giving 1° for 23*2 feet. 

 At the same depth in rock in another level of the same mine the 

 temperature is such as to give a ratio of 1° in 47' 0. Here we have 

 unequivocally the evidence of the warming agency of the water cir- 

 culating in the mining-district of Cornwall. The temperature of 

 116° may be conceived to arise from a depth of 2200 or 2300 feet — 

 or 800 feet below the floor of the mine. 



The surface of the earth is, in fact, now more heated by con- 

 vection of heat up its cracks and fissures than by conduction through 

 its sohd masses. In earlier geological times these cracks and fissures 

 were undoubtedly more open than now : for many reasons it is con- 

 ceivable that the circulation of water was both more abundant and 

 more rapid ; and thus, exactly as our greenhouses are warmed by 

 hot-water pipes, it is supposable that the ancient earth-surface was 

 warmed by currents along the innumerable void spaces now in part 

 filled by the sparry and mineral matter left by those very waters, 

 which have thus contracted or obhterated their own channels, but 

 have left monuments not to be neglected in reasoning on the ancient 

 condition of the earth. 



Once clearly in possession of this view of the pervading action of 

 water heated by the rocks which it traverses, and of the considerable 

 depths which it reaches in countries far from volcanos, and the 

 great depths to which it penetrates in those countries, we turn with 

 interest to these inquiries of modern times which have disclosed the 

 chemical results attainable by water under such conditions. 



From careful personal inspection, Bunsen arrives at the conclusion 

 that none of the rocks of Iceland are capable of resisting the action 

 * Fox, in Keport of British Association, 1857. 



