ON THE LEAD MINING DISTRICTS OF YORKSHIRE. 171 
to be influenced, that are peculiar to the Mines of our three Northern Dales, 
while certain characteristics more particularly pertain to our Southern Mi- 
ning Fields. We may, therefore, for all the purposes of this paper, treat the 
Lead Mines of this county, as belonging to two great Mineral Districts, the 
Northern and the Southern. 
In each district we have the Rake, the Pipe, and the Flat Veins. The 
ores from the Pipe and Flat Veins are generally found more fusible in the 
furnace, and to yield a higher per centage of lead, than those from the Rake 
Veins; and the ores from the Limestones (whether produced from the 
Rake, Pipe, or Flat Vein) are found to be more easily reduced, and to make 
a much better quality of metal for White Lead, than those from the Grit- 
stone. 
Here, I would refer to a correspondence, which took place some few 
months ago, in the columns of the ‘ Mining Journal,’ on the subject of Slick- 
ensides. It was there asserted that Slickensides had never been met with 
in Gritstone. I am prepared to meet this assertion, by the production of 
the specimen obtained from the Gritstone in the Grassington Mines; and 
with the exception of one from the same place, which I gave to the late 
Duke of Devonshire, I much question there being a better specimen in the 
country. 
The Slickensides first appeared at the point of junction of two veins, and 
continued their course in a perfectly straight line in the centre of the joint 
vein, for about 70 yards in length; or they might perhaps more correctly be 
said to have still divided the two veins, forming the North side of the one, 
and the South side of the other. (See fig. 7.) 
We could have procured specimens from either side, with as good a sur- 
face as the one exhibited, but not so large. It was only from the South 
side that they could be obtained of any size, the other being so cracked 
horizontally, that it was seldom a piece could be broken off, more than 
an inch or two wide ; in fact, the cracks on this side were almost as nume- 
rous as the striz on the surface of the North. 
The vein, throughout the whole length in which the Slickensides were 
found, maintained nearly a perpendicular position; and the striz were as 
nearly horizontal. In many parts of the vein, we had the thickness of a foot 
of solid ore behind each face of Slickenside. 
Many present will no doubt have read or heard of the phenomena reported 
to have attended the laying open of Slickensides in Germany; that the 
miner has at times been much frightened by the loud reports occasioned 
by the explosions. 
When driving our level in the Slickensides, we generally worked forward 
‘on the North side, leaving the South, or strong side, standing for 6 or 8 yards 
in length ; and on more than one occasion, the warkmen spoke of the reports 
they heard, sometimes as loud as that of a small pistol. At such times, 
numerous places could be seen where pieces had been blistered, and blown 
way from the face of the Slickenside; which presented much the same ap- 
pearance as a wall recently plastered with very imperfectly-slacked lime, but 
on a much larger scale. 
The ore from a vein carrying much Slickenside, requires generally a 
higher temperature, and is altogether more refractory in the furnace than 
that from one free from it. 
_ As a general rule, the greatest number of veins in each Mining district 
are found to run nearly parallel to each other. There are others that form 
a gles more or less acute, with the predominant direction; which, in the 
Northern District, is a little North of East, and South of West; whilst in 
NZ 
