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 i 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. ili. of the Zransactions 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 extending. 
The medium of its transportation is supposed to be the salt 
spray, which, in stormy weather, is known to be wafted to a 
ereat distance. The sand consists chiefly of very finely com- 
minuted shells, which, when once deposited by these natural 
air-balioons 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 fhe granitic range of Dartmoor, is scarcely fifty 
miles. Ce ertainly, few countr ies in the world offer so many 
facilities for studying the science of geology as our own. 
