661 
Many veins, particularly in our more northern fields, have 
a tolerably direct course for a considerable distance. The 
Old Gang vein, in Swaledale, has been worked for many 
miles in length, and can be traced to a much greater 
distance in nearly a straight line. 
In the three northern fields, viz. : — Swaledale, Arkendale, 
and Wensleydale, the veins are more regular in size, and 
the beds of a more uniform thickness, than in the three 
southern ones. In the former, the calcareous beds have 
been the principal sources of produce, while our southern 
mines have their principal deposit in the gritstone. 
There are many other peculiarities which strongly dis- 
tinguish the veins and beds of our northern dales from 
those of the southern ; and we may accept this natural 
division of the Yorkshire mines into two great classes, as 
sufficiently defined for our present purpose. The rake, 
ie pipe, and the flat vein, appertain to each district. 
Ores from the pipe and flat veins are much more 
fusible than from the rake ; and the ores from the lime- 
stone beds are in like manner preferable to those from the 
gritstone. 
It has been asserted that Slickensides has never been 
found in the gritstone. The specimen now produced proves 
the fallibility of this conclusion ; being obtained from the 
"grit" in the Grassington mines, where it was found, 
forming the only division between two veins for about 
seventy yards in length. 
The major part of veins in each district are nearly 
parallel to each other, while the remainder run counter 
to, and. form intersections with them. The predominant 
direction in the northern district is north of east, and 
south of west ; while in the southern fields it is north 
of west, and south of east. The former, or " right 
running veins," when intersected by the counter or 
