THE INFLUENCE OF GEOLOGY ON HORTICULTURE. 399 



covered with heath, coarse grass, and peat, as on Dartmoor, forming 

 either a bare sandy soil or a cold, stiff, and wet clay. Where, however, 

 the elevation is less and the climate drier, as at Moreton Hampstead, on 

 the eastern side of Dartmoor, the soil improves, forming useful pastures 

 and arable land from which the potatos sold in Exeter market are 

 obtained ; on the west of Dartmoor there is also fine pasture letting at 

 GOs. per acre. The soil of the Scilly Isles is good and largely used for 

 daffodil growing ; this soil is derived from a granite which, in addition to 

 quartz, felspar, and mica, contains hornblende, which, on decomposition, 

 yields lime, magnesia, and oxide of iron. 



Volcanic Bocks include the greenstone, basalt, serpentine and syenite, 

 and these, when disintegrated, usually form good soils. These rocks occur 

 as serpentine in the neighbourhood of the Lizard, in Cornwall, where 

 they give rise to soils of an inferior quality owing to the amount of 

 magnesia, but hornblende rock in the same district yields an extremely 

 fertile soil ; as greenstone in Charnwood Forest ; as syenite at Mount 

 Sorrel and in the Malvern Hills ; as porphyry in the Cheviot Hills, 

 Cumberland, Anglesea, and Carnarvon. 



The lowest of the primary rocks are the Cambrian and Silurian ; 

 these come to the surface over a large portion of Wales, both in the 

 north and the centre, and in the Lake District in parts of Cumberland, 

 Westmoreland, and Lancashire. 



The Cambrian Bocks, in the West of Wales and Cumberland, occur 

 chiefly in mountainous districts. The rock is largely of a slaty descrip- 

 tion, weathering slowly into poor thin soil or cold clay, covered chiefly by 

 heath and bog. The soils are very deficient in lime. 



The Silurian formation comes to the surface in Denbigh, Montgomery, 

 and Radnor, and skirts the south and east of Carmarthen, the north of 

 Hereford, and the south of Shropshire. Much of this formation consists 

 of deep beds of sandstone and shale, the former covered with heath, the 

 latter producing cold muddy clays. The Llandeilo Mags, which contain 

 lime, form a fertile arable soil in the south of Carmarthen, especially on 

 the banks of the Towy. This is also the case in Herefordshire and 

 Shropshire, where the Aymestry and Wenlock limestones, mingling with 

 the rocks below and above, produce fertile soil. 



The Old Bed Sandstone is ever associated with Hugh Miller, the 

 Cromarty stonemason, who became one of the greatest of geologists, 

 notable for careful observation and poetic description. This formation, 

 though occasionally of vast thickness, estimated at varying between 500 

 and 10,000 feet thick, does not occupy a very extensive area at the 

 surface. It consists of red sandstones and marls. These rocks form a 

 portion of Pembroke and Carmarthen, the greater part of Brecon and 

 Hereford, and parts of Monmouth and Glamorgan ; and the north and 

 south of Devon and much of Cornwall rests on this formation. The 

 upper and lower beds often produce hungry, barren, sandy soils, but the 

 middle beds in Hereford, South Devon, and parts of Cornwall produce 

 excellent land, as they contain more clay and lime. Tenbury, in 

 Worcestershire, noted for its cherries, stands where the Old Red Sand- 

 stone is mixed with alluvial deposit. 



Sir Roderick Murchison wrote of this formation : — " The most loamy 



