ae ae be ae ee ee 
+ On the Bristol Copper Mine. 367 
In reflecting upon the probable cause of the decomposition of 
this extensive bed of talco-micaceous rock the suggestion natu- 
rally arises that.it has probably a close connection with the injec- 
tion of the trappean rocks among and beneath the sandstones of 
= secondary. "This event it is certain was a subaqueous one, 
e 
water must have left its traces in chemical changes produced by 
so powerful an agency. The irruption of the copper ores may 
have been and probably was an earlier event of segregation. But 
if the cause adduced for the decomposition of the flucan is the 
true one, it is pretty certain that the same decomposed material 
will be found at the greatest depth to which the mine will ever 
be explored. As it is now proposed to sink a shaft in the sand- 
stone to the depth of 600 feet and to connect it at every 60 feet 
with the flucan by a cross-cut, we shall have the opportunity of 
studying these phenomena in ‘detail as the explorations proceed. 
it is rather remarkable that the line of actual contact between the. 
sandstone and the crystalline rocks is seldom visible and has still 
more rarely been carefully explored. - We do not know of another 
example where this important feature in our geology has been 
explored with so much care as in the case before 
Many statistical data embodied in our report a which are 
ed 
chiefly of economical value, are  omitt ere. It is proper to 
ee § however, that an important item in the present pts future 
success of this mine is the employment of new and improved 
machinery, the most important of which are the ore seonsaies 
and patent jigs, invented by Mr. H. Bradford. The separator is 
a shaking table of entirely new form and construction, on which 
by the rapid reciprocal motion of a copper plate the ore is by aid 
of water and gravity, thrown over one edge while the waste is 
projected over the other. After giving in detail the statistics of 
their operation, our report holds the following language 
Undoubtedly Bradford’s separators are the most most important me- 
chanical invention ever produced for dressing what are called 
slime ores. The principle upon which they are constructed is 
truly philosophical, and has been most pyctirtae applied by pie 
talented inventor to the production of tt is machine. Like 
accurate instruments they require careful adjustment in all ae - 
ticulars, but once adjusted they are completely ce so that 
one attendant can easily oversee at least twenty of them 
Our re ” concludes with the following observations— 
In reviewing the condition of the Bristol na at the present 
a che! following are the most noteworth 
e mine is one of the few in the United | States which is 
now tet at a profit. 
