118 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
Then, What is the action whereby the segregating calcareous matter repels 
the hematitic,—thus operating as a pseudo-bleacher ? 
And lastly, How comes it that the one set of rents are lined with ae ‘yte, with 
vacuous interspaces ; while that which lies at right angles thereto contains no trace 
of baryte, but is totally filled with a clay-like material ? 
An explanation which may be said to lie upon the surface—namely, that the 
first mentioned set had been of earlier formation, and had been the seat of a 
process which had reached its termination before the formation and filling up 
of the latter,—does not meet the facts of the case, because the rock-rents which 
form the “ backs” seem to have been antecedent to those existing as “cutters ” ; 
for the former pass numbers of the latter, while these but very seldom cut 
across the former. 
The rock seems to be sti// purveying hematitic and chloritic matter to the 
cracks which form its “faces” ;—is there a polarity in the guidance of its 
decomposition, acting so as to fill its minor and secondary rents with barytes 
and with copper,—-enabling them at the same time to reject the slimy plug 
which chokes the backs, that they may at least aspire to the dignity of being 
true mineral veins ? 
Some questions of weighty mining import might possibly be answered 
through a study of this narrow field ;—the points of chief mineralogical interest 
are the occurrence of a chloritic mud in a form simulating glauconite,—and the 
singular manner in which a large quantity of chlorite may be entirely masked 
by a comparatively small quantity of peroxide of iron. 
