30 
formations, but there are many others where it is question- 
able. Gustav Bischoff points out in his “Chemical and 
Physical Geology” that “ It is certain that the contents of 
a lode are of later date than the adjoining rock, so that it 
can be shown that these contents originate from the adjoin- 
ing rock, and if it can be ascertained what compounds of 
the metal exist in that rock, the previously existing mine- 
rals may be distinguished from those of later date ; but the 
determination of this point is attended with great difficul- 
ties and is generally impossible.” It is a well ascertained 
fact that all the ores of copper are found mostly in crystal- 
line rocks or metamorphic rocks derived from them (some 
ores however being found in newer formations); and Struve 
(Ueber die Nachbildung der naturlichen Heilquellen, Heft 
2, 17) has proved in the most conclusive manner that 
granite, porphyry, phonolite, gneiss, basalt, clay slate, 
trachyte, &c., contained a more or less appreciable amount 
of sodium chloride, and it is also well known that nearly 
every spring water flowing from rocks contains sodium 
chloride or a chloride of one of the alkaline earths (magne- 
sium chloride). Further, it has been shown by Delesse 
(Jahrb. f. Min. 1862, 605) that all rocks are saturated with 
water, and it is also a well ascertained fact that iron pyrites 
(FeS 2 ) is disseminated throughout all crystalline rocks. 
Having these facts before me, I made an experiment in 
order to ascertain what reactions would occur on heating 
iron pyrites and a solution of cupric chloride together in a 
sealed tube at a moderately high temperature. Small pieces 
of pure iron pyrites were placed in a glass tube, then covered 
with a moderately strong solution of pure cupric chloride, 
and the tube sealed up and heated for 14 days at a tempera- 
ture varying from 135° — 210° C., but the greater part of the 
time the temperature oscillated between 150° and 170°. On 
the seventh day the colour of the cupric chloride had 
become considerably lighter, and a small deposit of violet-red 
