24 Connection between Geology and AijrkuHurc in 



a northern aspect, would be speedily swept away, or be contorted 

 and stunted in their growth, if exposed to the full force of the 

 same winds. 



Though, from the want of friction, beyond that which they 

 receive from the surface of the sea, the prevalent sea-winds act 

 most severely on the coast vegetation exposed to them, preventing 

 that growth which adjacent sheltered spots show the decom- 

 position of the same rocks to be capable of supporting, their 

 influence is not confined to the coasts, but extends inland in pro- 

 portion to distance from the sea and height above it. Many a 

 valley, therefore, in a given range of rocks, is comparatively fer- 

 tile ; while the high grounds in the same range make a poor 

 return for the labours of the agriculturist. 



The chalk of the district is seldom exposed on the surface, and 

 therefore contributes little by decomposition to the superjacent 

 soil ; hence we find no area of importance presenting the marked 

 agricultural character of the chalk portions of the adjacent 

 counties on the eastward. The chalk and green-sand are, indeed, 

 generally so completely covered by gravel that the parts represented 

 in maps as composed of these rocks afford a very common agricul- 

 tural character, and cannot, on the whole, be considered fertile. 

 Downs of heath and furze are very common upon these gravels ; 

 and those portions cultivated as arable land abound in flints and 

 fragments of chert. The gravels also frequently contain much 

 clayey matter intermingled with them, so that water does not 

 readily percolate through them, and black peaty soils are often 

 observed. In places where marls, probably the remains of the 

 plastic clay beds, are found near the surface, the agricultural 

 character of the land above the chalk and green-sand is much 

 improved, and the country more fertile. In those situations in 

 the Black Downs, where the gravels have not descended thickly 

 spread over the sides of the hills upon the red marls, or lias, 

 beneath the green-sand, the contrast offered between the agri- 

 cultural condition of the country, u})on the one and the other, is 

 remarkably striking ; indeed, a well-marked line of heath and 

 common nearly coincides with the division between the two rocks. 

 Haldon Hills also afford good examples of the contrast between 

 the vegetation upon the green sands, with their gravel covering, 

 and upon the rocks beneath them. 



When the agricultural character of the lias Is compared with 

 that of the red marl and sandstone adjoining it, a very striking 

 general superiority is observed in the latter. Good opportunities 

 for observing this circumstance are afforded by the Vale of Taun- 

 ton, where both rocks occur under similar general conditions as 

 to climate. It will be seen also in the neighbourhood of Bridge- 

 water^ in that of Watchet, and near Uphill and Worle, in the vici- 



