134 
rorULAR SCIENCE REVIEW. 
there is rock, mud, or sand. When the sand occurs only in the 
lower part it rarely becomes quite dry, and the wind has little 
or no effect upon it. But where sand occupies the whole of the 
foreshore, then that part at or near high water mark is dry for 
the greater part of the tide. The wind lifts the particles of 
sand and rolls them along. Where the coast is cliffy the sand is 
only blown against the cliff, to be again washed down by the 
rising tide ; but where the shore is low the wind carries the 
sand beyond the reach of the waves, and there it accumulates : 
this is the origin of blown sand. 
The seaward face of sand-dunes is generally steep. This is 
sometimes due to the base of the dune being cut away by the 
waves ; but much the same effect is produced on the side facing 
the wind when the waves do not reach the hills. In no case, 
however, does the slope exceed 30° with fairly dry and loose 
sand ; although the slope generally appears to the eye to be 
much greater than this. Dunes sometimes attain a great 
height. This is due to the sand being rolled by the wind along 
the surface and up the increasing slope, not to the wind rais- 
ing the grains of sand to any height above the surface. For 
this reason quite a small stream of water will often suffice to 
stop the progress of sand-dunes. The sand is blown into the 
water, but not over it ; and unless the sand so blown is suffi- 
cient to choke up the channel and dam back the stream, the 
sand cannot reach the further side. The fine dust of the desert, 
and of the Pampas, is carried to a great height by the wind ; 
but this is an almost impalpable powder. 
We will now describe the coast sand-hills of England, com- 
mencing with those on the north-east. The hills are nearly 
everywhere known as “ dunes but in various parts of England 
they go by other names — as bents, downs, denes, links, greens, 
towans, and starr-hills ; they are often called 66 warrens,” from 
the numbers of rabbits which inhabit them. The commonest 
plant of the dunes is the 44 bent,” or 66 starr-grass ” — Arundo 
(Ammophila) arenaria ; the long rhidome of which binds the 
sand, and greatly checks its movements. 
The “links ” of the Northumberland coast are often continuous 
for miles; they are usually only about 150 yards wide, but ex- 
pand in some places to 300 or 400 yards. The average 
height of the summits is about 40 feet above mean sea level ; 
but occasionally they rise to 60 or 70 feet. At the mouth 
of the little river Lyne there is a hill 87 feet high. Where 
these links occur, the adjacent ground is mostly flat, and the 
50- feet contour line is often half a mile or more from the 
shore. Although these links are of so small a height, yet, 
rising abruptly from the flat ground, they appear to be hills 
of no mean elevation. Some species of plants, which occur 
