78 Introduction to Geology, 



Professor Sedgewick's papers in the Annals of Philosophy, 

 on the alluvium and diluvium of the great fen district, con- 

 tain some valuable practical information on this part of the 

 series ; so, also, do the articles by Mr. Warburton and Mr. 

 Lyell, on the recent fresh-water limestone in Scotland, and 

 shell-marl in England, in the Transactions of the Geological 

 Society; and Dr. Buckland's paper on the alluvial products in 

 the basins of London and Hampshire. The influence of the 

 wind in accumulating sand, has been treated on in some 

 articles in the Philosophical Magazine for 1827. On the mar- 

 gins of our coasts, this process is not without its uses, and long 

 ranges of sand-hills, elevated by this means, protect the coun- 

 try from the encroachments of the sea. Occasionally, however, 

 it threatens to encroach upon the land. Mr. Hawkins men- 

 tions, in vol. iii. of the Transactions of the Geological Society 

 of Cornwall, that many thousand acres have been covered with 

 sea-sand on the northern coast of Cornwall. " The particles 

 of this sand have been wafted thither by the north-westerly 

 winds, which blow with such force on that side of the county ; 

 and this deluge of sand is said to be progressively extend:|.ig. 

 The medium of its transportation is supposed to be the salt 

 spray, which, in stormy weather, is known to be wafted to a 

 great distance. The sand consists chiefly of very finely com- 

 minuted shells, which, when once deposited by these natural 

 air-balloons on the higher grounds, are continually drifted to 

 leeward." 



We have thus taken a rapid survey of the principal divi- 

 sions into which the rocks, strata, and deposits, from the 

 earliest to the latest, are usually arranged. They comprehend 

 by far the greatest part of all that are known on the globe. 

 On looking at the small space which our island occupies, 

 and comparing the enormous expansion of these formations 

 on our continents, we cannot but regard it as a circumstance 

 of singular geological interest, that England should thus pre- 

 sent, within so limited an area, such an epitome of the globe. 

 In some points, the whole series of the strata, from the chalk 

 to the coal formation, may be crossed within the space of 

 twenty miles ; and the distance from the chalk hills of Dorset- 

 shire, and the granitic range of Dartmoor, is scarcely fifty 

 miles. Certainly, few countries in the world offer so many 

 facilities for studying the science of geology as our own. 



