a oy ‘ ~ 
324 DYNAMICAL GEOLOGY. [Boor TT. 
and fall over the steep slopes. Not only do the particles travel, but 
the ridges also more slowly follow éach other, as in Fig. 83. 
The western sea-board of Europe, exposed to prevalent westerly 
and south-westerly winds, affords many instructive examples of these 
eolian or wind-formed deposits. The coast of N orfolk is fringed 
with sand-hills fifty to sixty feet high. On parts of the coast of 
Cornwall,! the sand consists mainly of fragments of shells and 
corallines, and through the action of rain becomes sometimes 



3 
eS 
aesed, = Mas bs a3 
| 
Seer 

se Me 2G 
Sree a Se 
Fic. 83.—D1acraM OF RIPPLES IN BLOWN SAND. THE RIDGES b!, Lb’, b®, IMPELLED IN 
THE DIRECTION W W, SUCCESSIVELY coME To occupy THE HoxLows a’, a’, a* (B.). 
cemented by carbonate of lime (or oxide of iron) into a stone so 
compact as to be fit for building purposes. Long tracts of blown sand are 
likewise found on the Scottish and Irish? coast-lines. Sand-dunes 
extend for many leagues along the French coast, and thence, by 
Flanders and Holland, round to the shores of Courland and 
Pomerania, On the coast of Holland they are sometimes, though 
rarely, 260 feet high,—a common average height being 50 to 60 
feet. 
The breadth of this maritime belt of sand varies considerably. On 
the east coast of Scotland it ranges from a few yards to three miles ; 
on the opposite side of the North Sea it attains on the Dutch coast 
sometimes to as much as five miles. The rate of progress of the 
dunes towards the interior depends upon the wind, the direction of 
the coast, and the nature of the ground over which they have to 
moye. On the low and exposed shores of the Bay of Biscay, when 
not fixed by vegetation, they travel inland at a rate of about 164 
feet per annum, in Denmark at from 3 to 24 feet. In the course of 
their march they envelop houses and fields; even whole parishes 
and districts once populous have been overwhelmed by them.* 
Along the margins of large lakes and inland seas many of the 
phenomena of an exposed sea-coast are repeated on ascarcely inferior — 
scale. Among these must be included sand-dunes, such as those 
which, reaching heights of 100 to 200 feet on the south-eastern 
shores of Lake Michigan, have entombed forests, the tops of the 
trees being still visible above the drifting sand. Large dunes occur 
also on the eastern borders of the Caspian Sea, where the sand 
Ussher, Geol, Mag. (2), vi. p. 807, and authorities there cited. 
See Kinahan, Geol. Mag. vili. p. 155, 
On the growth of Holland through the operation of the wind and the sea, see 
Elie de Beaumont, “ Lecons de Géologie pratique,” i. 
* This destruction has been, during the last quarter of a century, averted to a great 
extent by the planting of pine forests, the turpentine of which has become the source of 
a large revenue. . 
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2 
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