28 Connection between Geology and AfjrlcuUurc in 



rocks in Devon and Cornwall are very commonly known by the 

 name of dim stone, the harder being not unfrequently termed iro?i 

 or ire stone, particularly in the latter county. Much of the vesi- 

 cular trap and trappean ash is known as honeycomb dim, espe- 

 cially in Devon, and land upon it is always highly esteemed by 

 the farmer. Mr. Worgan (' View of the Agriculture of Corn- 

 wall/ p. 10) observes, that wherever the dun, or ironstone, is met 

 with in Cornwall, "^it is deemed a fortunate circumstance, be- 

 ing a certain indication of the fertility of the incumbent soil." 

 Limestone occurs in sufficient abundance in the vicinity of Torbay, 

 Newton Bushell, and Plymouth, to afford an agricultural character. 

 The land upon it is generally considered good, but it is frequently 

 light, and, from the hardness of the subjacent rock (though its sur- 

 face is often broken into fragments from atmospheric causes), liable 

 to be washed away in exposed situations. In this respect it agrees 

 with the carboniferous limestone on the north of the district, near 

 Weston-super-Mare and Uphill, as might be expected from the 

 similarity of their mineral composition. The range of the red 

 and variegated slaty beds of the grauwacke may, upon the whole, 

 be considered as among the most productive of that series in 

 Cornwall and Devon, and very frequently much barley is success- 

 fully grown upon it. Thus, much barley, often malted, is ex- 

 ported from Kingsbridge and Padstow, grown upon the red and 

 variegated slates of the country adjoining those places. The red 

 slates, particularly when they contain some calcareous matter, are 

 favourable also to the growth of apples, as upon the banks of the 

 Dart and Fowey. 



As in the north, in those localities where the sandstones prevail, 

 there is less fertility than where slates occur. According to the 

 general mineral composition of the latter is also their character 

 of heavy or light ; those most approaching to clay slates being 

 liable, where the drainage is imperfect, to become clayey. They 

 generally support a fine growth of oak, as is well seen in the 

 numerous sheltered valleys of southern Cornwall and Devon. 

 The band of grauwacke, including the associated limestones and 

 trappean rocks, which ranges from Ashburton, Newton Bushell, 

 and Torbay, between the granite of Dartmoor and the mica slates 

 of Marlborough and Chivelstone, to Plymouth, and thence along 



description."— Johnston's Agricultural Chemistry, p. 386; where the ex- 

 ceptions to the general rule are stated. Dr. Bucldand informs me that, in 

 July, 1840, being on a visit at the place of Sir C. Menteith, Closehurn, in 

 Dumfriesshire, he observed on a moor lately reclaimed from heath, and 

 then covered with coarse grass, a band of bright emerald-green herbage 

 stretching across it. This band marked the underground course of a trap- 

 dyke, traversing slate-rocks, called Devonian, from their prevalence in 

 Devonshire. — Ph. Pusey. 



