Ixvi REPORT — 1864. 



than before the Wheal- Clifford hot spring was analyzed, it may become of 

 high value. According to a rough estimate which has been sent to me by Mr. 

 Davey, the Wheal-Clifford spring yields no less than 250 gallons per minute, 

 which is almost equal to the discharge of the King's Bath or chief spring of 

 this city. As to the gases emitted, they are the same as those of the Bath 

 water — namely carbonic acid, oxygen, and nitrogen. 



Mr. Wartngton Smyth, who had already visited the Wheal-Clififord lode 

 in 1855, re-examined it in July last, chiefly with the view of replying to 

 several queries which I had put to him ; and, in spite of the stifling heat, 

 ascertained the geological structure of the lode and the exact temperature of 

 the water. This last he foimd to be 122° Fahr. at the depth of 1350 feet ; 

 but he scarcely doubts that the thermometer would stand two or three 

 degrees higher at a distance of 200 feet to the eastward, where the water is 

 known to gush up more freely. The Wheal-Clifford lode is a fissure varying 

 in width from 6 to 12 feet, one wall consisting of elvan or porphyritic 

 granite, and the other of kiUas or clay-slate. Along the line of the rent, 

 which runs east and west, there has been a slight throw or shift of the rocks. 

 The vein-stuff is chiefly formed of cellular pyrites of copper and iron, the 

 porous nature of which allows the hot water to percolate freely through it. 

 It seems, however, that in the continuation upwards of the same fissure 

 little or no metalliferous ore was deposited, but, in its place, quartz and other 

 impermeable substances, which obstructed the coui'se of the hot spring, so as 

 to prevent its flowing out on the sui-face of the countiy. It has been always 

 a favourite theory of the miners that the high temperatm-e of this Cornish 

 spring is due to the oxidation of the sulphurets of copper and iron, which are 

 decomposed when air is admitted. That such oxidation must have some 

 slight effect is undeniable ; but that it materially influences the temperature 

 of so large a body of water is out of the question. Its effect must be almost 

 insensible ; for Professor MUler has scarcely been able to detect any 

 sulphuric acid in the water, and a minute trace only of iron and copper in 

 solution. 



When we compare the temperatm-o of the Bath springs, which issue at a 

 level of less than 100 feet above the sea, with the Wheal-Clifford spring found 

 at a depth of 1350 feet from the surface, we must of course make allowance for 

 the increase of heat always experienced when we descend into the interior 

 of the earth. The difference would amount to about 20° Fahr., if we adopt 

 the estimate deduced by Mr. Hopkins from an accurate series of observations 

 made in the Monkwearmouth shaft, near Durham, and in the Dukinfield 

 shaft, near Manchester, each of them 2000 feet in depth. In these shafts 

 the temperatiu-e was found to rise at the rate of only 1° Fahi-. for fiyerj 

 increase of depth of from 65 to 70 feet. But if the Wlieal-Clifford spring, 

 instead of being arrested in its upward course, had continued to rise freely 

 through porous and loose materials so as to reach the sm-face, it would 

 probably not have lost anything approaching to 20° Fahr., since the re- 

 newed heat derived fi-om below would have warmed the waUs and contents 

 of the lode, so as to raise their temperature above that which would naturally 

 belong to the rocks at corresponding levels on each side of the lode. The 

 almost entire absence of magnesium raises an obvious objection to the hypo- 

 thesis of this spring deriving its waters from the sea ; or if such a soui'ce be 

 suggested for the salt and other marine products, we should be under the 

 necessity of supposing the magnesium to be left behind in combination with 

 some of the elements of the decomposed and altered rocks through which the 

 thermal waters may have passed. 



