GEOLOGY, BY DR. BOASE.
The whole of this parish, with the exception of a small patch of slate at Rosemodris, rests on granite. Judging from what occurs in the eastern part of Cornwall, one might be led to expect that the land of St. Burian must be sterile. In some elevated spots it undoubtedly is so, but in general the parish is well cultivated and highly productive.
This difference in the granitic soils of east and of west Cornwall, maybe, in part, explained by the gradual diminution of height towards the west, accompanied by a corresponding improvement of the climate; but in this part of the county more of the debris, especially of diluvial clay, is retained on the surface, that of the more elevated eastern ridges having been in great measure swept away.
This circumstance must not, however, be omitted. The granite of Burian exhibits more varieties than have been yet found in the eastern district. The slate in the cliffs at Rosemodris is a felspar rock, and its contact with the granite is distinctly seen; where it may be observed at the eastern extremity traversed by numerous granite veins; and the granite near this junction abounds in shorl.
NOTE BY THE EDITOR.
Doctor Paris has remarked on the granite of this district, that it contains full twenty-five per cent of felspar, which he says at once explains the rapidity of this stone's decomposition, and the fertility which is so very unusual in granitic countries; and that this granite in a state of decomposition, when it is provincially called growan, has actually been applied to some lands as a manure, and with the best effect.
I had the pleasure of attending Doctor Withering (author of the Arrangement of British Plants, &c.) to