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tions. If on the map we measure ten miles east and 
ten west from Ilkley, on a line bearing 12° north of east 
and south of west; and at right angles to this base, 
draw lines northward thirty-five miles from the two points 
so obtained, we shall, in this area of 700 square miles, include 
the high grounds bounding Airedale, Wharfedale, Nidder- 
dale, Wensleydale, Arkendale, and Swaledale 3 in which 
the principal lead mining fields of Yorkshire are situate. 
The strata throughout this area, are the lower members 
of the carboniferous series. Though the same class of rock 
prevails throughout the lead bearing districts, each individual 
stratum does not always occur in neighbouring mines, while 
the thickness of each bed is exceedingly variable. 
In the metalliferous portion of the carboniferous rocks, 
we have the rake vein, the pipe or tube vein, and the lateral- 
embedded or flat vein. The first appearing as a rent or 
fissure through the strata, of a great length, and generally 
to an unknown depth. The pipe vein has the form of an 
irregular cylindrical tube, is met with in certain strata, 
(generally limestone), and dips with the beds, or passes more 
or less diagonally through them for a great length. The 
third, or flat vein, is seldom met with except in connection 
with a rake vein, but has always a position conformable to the 
stratum in which it is embedded. Rake veins are by far 
the most numerous in every district, and their phenomena 
the most varied and complicated. The greater portion of 
our lead ore is likewise from them. The " bearing" of 
a rake vein is seldom a perfectly straight line, but 
generally approximates thereto in its entire length. The 
"hade" or inclination varies considerably in the angle 
formed with the vertical. It is likewise more horizontal 
in the soft or argillaceous beds, than in the hard and 
solid rocks; while, frequently, in passing a thin seam of 
coal, or of soft clay, it flats away with the stratum for a 
