562 



BLOWN SANDS. 



Enough has now been stated to show, that in this region, the present erosive action of 

 water upon hard rocks is confined to the mountain tracts. At the same time, it must 

 he recollected, that our Silurian rivers, even after they quit the mountains, though no 

 longer employed in transporting stones and coarse gravel, are very active agents in 

 carrying away a large proportion of the earth's surface in the form of sand and mud. 

 No European river of equal magnitude is charged with a larger amount of turbid 

 sediment than the Severn, — the result of its own long course (and of those of its tri- 

 butaries) through tracts of mudstone, marl, and soft sandstone. Such rocks being 

 easily decomposed and degraded, have afforded those finely levigated materials, a por- 

 tion of which has added new lands on the banks of the river 1 ; but by far the larger 

 quantity has been borne away into the great estuary of our Island. The shoals there 

 accumulated during past ages, and still depositing, may hereafter be examined, if other 

 changes of the relative level of sea and land shall take place ; and future geologists may 

 then study the sub-aqueous formations of our own gera. 



Blown Sands. — Submerged Forests, 8fc. 



Among the phenomena of modern date must be noticed blown sands and submerged 

 forests. The former occur extensively on the coasts of Pembrokeshire and Caermar- 

 thenshire. Between St. David's and White Sand Bay they cover hills at heights of 

 more than 1 50 feet above the strand, and are prolonged upwards of a mile inland among 

 the slaty rocks. Again, at the mouths of the bays of Freshwater east and Freshwater 

 west, as well as at points of the Stackpole promontory, are great heaps of this sand, 

 which, in places, present escarpments 30 and 40 feet high. These sands contain a 

 prodigious quantity of land shells, including Helix aspersa, H. virgata, H. rufescens, 

 and Bulimi of 3 or 4 species. It might naturally be supposed, that these sands are still 

 increasing ; but such is not the case ; for many of them appear to have been stationary 

 during long periods. On the summit of the slaty coast cliffs at St. David's stands a 

 ruined chapel, around which and far beyond it inland, much blown sand has been 

 heaped up, while the sides and floor of the building are free from it. Again, at Newton 

 Burrows a ridge of Old Red Sandstone is surmounted by a cromlech (half a mile distant 

 from the shore), and yet this low erection, though environed by dunes of sand much 

 higher than itself, has not been covered over. In Pembrokeshire, therefore, local 

 causes, which were in action at remote periods, must have been discontinued, in one 

 instance before the Druids erected their cromlech, and in the other before the monks 

 built their chapel; and in neither case has the sand advanced beyond its ancient limit. 

 The cessation of the action which formed these dunes is further proved by the form 

 of the ground, for at Newton Burrows the sand is heaped up in spots higher than the 



j See note 1, p. 450, in which the rapid formation of new land on the hanks of the Severn is pointed out. 



