Sir C. Lyell on the Mineral Waters of Bath. 21 
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 perco- 
late freely through it. It seems, however, that in the continua- 
tion upward of the same fissure, little or no metalliferous ore 
was deposited, but in its place, quartz and other impermeable 
substances, which obstructed the course of the hot spring, so as 
to prevent its flowing ort on the surface of the country. It has 
been always a favorite theory of the miners that the high tem- 
perature of this Cornish spring is due to the oxydation of the 
sulphurets of copper and iron, which are decomposed when air 
is admitted. That such oxydation 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 Miller 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 temperature of the Bath springs, which 
issue at a level of less than 100 feet above the sea, wit e 
Wheal-Clifford spring found at a depth of 1850 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° F., 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 temperature was 
found to rise at the rate of only 1° F. for every increase of dept 
of from 65 to 70 feet. But if the Wheal-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 sur- 
face, it would probably not have lost anything approaching to 
20° F., since the renewed heat derived from below woul ve 
warmed the walls 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 hypothesis of this spring deriving its waters from the sea ; 
or if such a source be suggested for the salt and other marine 
Precious metals, gold, silver, and platinum, as well as of tin, cop- 
per, lead, and many others, a slight trace of copper in the Bath 
