The
consideration of this change will further illustrate the operations of
nature in placing that which had been at the bottom of the sea above its
surface.
Strata, that are in one place regularly inclined, may be found bended,
or irregularly inclined, in following their course. Here then is a
source of irregularity which often materially effects the estimates
of miners, judging from what they see, of those parts which are to be
explored; and this is an accident which they frequently experience.
But, without any change in the general direction of the stratum, miners
often find their coal broke off abruptly, those two parts being placed
upon a higher and lower situation in respect to each other, if flat
beds, or separated laterally if they are edge seams. This is by miners
termed a _slip, hitch_, or _dyke_.
These irregularities may either be attended with an injected body of
subterraneous lava or basaltes, here termed whin-stone, or they may not
be attended, at least apparently, _i.e._ immediately, with any such
accident. But experienced miners know, that, in approaching to any of
those injected masses of stone, which are so frequent in this country,
their coal is more and more subject to be troubled.
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