32 Connection belwcen Geology and Agrkullure in 



racter of the subjacent granites, and, consequently, in tlieir relative 

 productiveness ; but, nevertheless, there is a constant and pre- 

 vailing kind of granite which readily decomposes, and forms a 

 large part, with the exception, probably, of the Hensborough boss, 

 of that to be found in the whole of them. Between the relative 

 fertility of the soil above this granite, according to locality, very 

 useful comparisons may be instituted. Dr. Boase has indeed 

 already remarked that the fertility of the granitic groups of 

 Cornwall gradually increases as they diminish in elevation,* an 

 observation which may very properly be extended to Devonshire. 

 The granitic or growan soil is one which frequently requires 

 rain, of which, however, there is no want generally in the district, 

 and the grass grown upon it is considered good for feeding cattle. 

 Under fair conditions as to height and exposure, it is very com- 

 monly celebrated for producing good potatoes. | Barley and oats 

 are chiefly cultivated upon it where employed for arable land, 

 wheat being rarely a successful crop except in a few situations, 

 among which St. Mary's, Scilly, and land in the parishes of 

 Burian, Sennan, and St. Leven, in the Land's End district, are 

 the most remarkable. J Oaks, ash, and sycamores grow well 

 upon the growan soils in sheltered situations, and where sufficient 

 attention is paid ; of which the grounds of Trebartha Hall, near 

 North Hill, afford as good an example as any we can select. 



Peat is very common upon the granitic soils, more especially 

 where the land rises high. Dartmoor produces a large quantity 

 of this substance, which is much employed as common fuel in the 

 country adjoining it. 



It has been considered that, at the junction of the granite and 

 slates in Cornwall, the soil is considerably improved by the mix- 

 ture of the decomposed portions of each rock ; and Dr. Paris states 

 that this fact is very observable in many places, more particularly 

 pointing out the superior fertility of this kind of junction at 



* Trans. Geol. Society of Cornwall, vol. iv. p. 365. 



t Mr. Worgan observes that "if Cornwall does not grow wheat enough 

 for its inhabitants, it certainly has the merit of supplying other counties 

 with large quantities of potatoes." — (View, &c., p. 75.) He further remarks 

 tliat, not only are many thousand bushels annually sent to Plymouth and 

 Portsmouth, but that (in 1808) some shiploads were exported to London. 

 Much of this produce is grown upon the growan soils, and the export would 

 appear as considerable as ever. Indeed large quantities are now fonvarded 

 to London by the Dublin steamers which touch at Falmouth, and early 

 potatoes are thus introduced abundantly into the London market. The 

 vicinity of Penzance contributes largely to this early produce, chieliy there 

 o-rown, however, upon the greenstone soils. 



+ Mr. Worgan states (' View of the Agriculture of Cornwall,' p. 9) that 

 from 40 to 45 Winchester bushels of red wheat per Cornish acre have been 

 raised upon the lands of these three last-mentioned parishes, the Cornish 

 being larger than the common statute acre in the proportion of about 6 to 5. 



