The junction of the granite with slate is concealed by a large track of marsh and bog; adjoining to which is a dreary waste of common, resting on an irregular bed of quartzose gravel, derived from the granite hills, and evidently of diluvial origin. This eastern part is sterile, merely affording a scanty subsistence to cattle during the summer. The remainder of the parish is composed of felspar and hornblend rocks, traversed here and there by courses of granitic elvan, a rock in every respect similar to that occurring in the granite. One of these courses may be seen by the road side near the rivulet of Pencarrow. Here the country is wooded and cultivated, exhibiting some picturesque scenes of hill and dale; so characteristic of the hornblend rock near granite.
St. Agnes is situate in the hundred of Pyder.
At the time of the Conqueror's tax there was no such parish or district as Saint Agnes; but the same passed in rates under the jurisdiction of the Earl of Cornwall's manor, now Duchy, of Twarnhayle; together with Peransand: which now parish of St. Agnes was taxed to the four shillings in the pound land-tax, 9th William and Mary, 1696, 137£. 5s.
The present church of St. Agnes was of old only a small free chapel dedicated to her, without endowment, till the same was augmented and rebuilt, of three roofs, as it now stands, by charitable collections, and the proper charge and cost of the inhabitants thereof, in 1484; consecrated and dedicated to the honour of Almighty