The north-eastern part of this parish extends to the east of Kitt
Hill, the most elevated point of Hingston Downs, which is composed of
granite. The slate adjoining thereto resembles that which occurs in
similar situations in the parishes of St. Austell and St. Blazey; and
this district has been the scene of considerable mining speculations.
In former ages it abounded in stream tin to such an amount that the
Cornishmen of those days expressed their opinion of its value by the
distich
Hengsten Down, well yrought
Is worth London town, dear ybought.
_Carew, Lord Dunstanville’s Edition, p. 272._
As the town of Callington is approached, the slate becomes of a darker
blue, and passes into hornblend rock, which prevails in the other
parts of the parish, and in several places so much abounds in quartz
as to form barren downs. This rock, however, has not any marked
character, and it is not often exposed to view; near St. Ive it
appears to graduate into the calcareous series.