Under the head of St. Cleather, a peculiar calcareous rock was
noticed, consisting of a variety of hornblende and calc spar, either
distinctly conjoined in a granular or laminated form, or so intimately
blended, as to form an homogeneous green rock. A large bed of this
peculiar rock occurs at Grylls or Garles, near the western boundary of
the parish. An attempt was made here to burn this rock as a limestone
for agricultural purposes; but after several trials it was abandoned;
for, unless great care be taken in selecting those parts alone in
which calc spar mainly abounds, the whole charge of the kiln
vitrifies, or runs into a slag, owing to the great fusibility of
hornblende, the other constituent of this calcareous rock.