On Mineral Ves. 245 
along with them the various metals—no such thing as dry 
sedimentary rocks exist naturally—for they all contain a 
certain amount of water, which fills up their pores, and 
affords an ample medium for the decomposition and trans- 
port of minerals—a road along which they may travel great 
distances. That this road does not remain unused is proved 
by the recent deposits of ore sometimes found in old mining 
works. 
A marked instance came under my notice at the Tees-side 
mine, where there was an old level driven on the vein in the 
limestone rock, which had not been used for nearly sixty 
years. In one part of this level a crop of carbonate of lead 
was formed, growing out of the old underlay wall of the 
vein in long, delicate, needle-like crystals. Had the growth 
gone on at the same rate, the wall of the vein would have 
been covered with a sheet of carbonate of lead about an inch 
thick in the course of a few hundred years. This is far from 
being a solitary case, as there are few men having much 
experience in practical mining on old fields who could not 
recount similar instances of modern deposits forming in old 
workings. ‘These recent deposits of metallic ores could not 
have been indebted to sublimation for their origin, nor to 
currents of water circulating in the vein fissure, as the water 
had been drained off by the level. It must, therefore, be 
evident that they could only have been derived from the 
rocks bounding the vein. 
Coming to the gold deposits of this colony we have 
modern auriferous pyrites of recent date formed in the gold- 
bearing drifts, and the experiments, particulars of which 
have been communicated to the Society by Messrs. Wilkin- 
son and Newberry, indicate how this has been effected. 
These views, as to the source from whence the ores have 
been derived, receive strong support from most of the 
phenomena presented by mineral veins. 
The veins in the limestone rock are usually accompanied 
by strings (joints filled with ore) passing out of the vein, 
and coming back to it after they have run a greater or less 
distance. (¢ e, Fig. 6.) Sometimes a portion of the wall 
of the vein is traversed by these joints of ore, set so close 
together as to render it profitable to work ; and the riders 
are frequently of the same character, the ores in some 
instances being intermixed with the compact rock, in others 
collected into a net-work of strings. In the north of England 
the beds in which the veins bear ore are generally separated 
