GEOLOGY. 251 
cause precipitation of vapour, when abundant, is rendered 
matter of ocular demonstration in that very striking 
phenomenon so common at the Cape of Good Hope, where 
the south or south-easterly wind which sweeps over the 
Southern Ocean, impinging on the long range of rocks 
which terminate in the Table Mountain, is thrown up by 
them, makes a clean sweep over the flat table-land which 
forms the summit of that mountain (about 3850 feet high), 
and thence plunges down with the violence of a cataract, 
clinging close to the mural precipices that form a kind of 
background to Capetown, which it fills with dust and 
uproar. A perfectly cloudless sky meanwhile prevails 
over the town, the sea, and the level country, but the 
mountain is covered with a dense white cloud, reaching to 
no great height above its summit, and quite level, which, 
though evidently swept along by the wind, and hurried 
furiously over the edge of the precipice, dissolves and 
completely disappears on a definite level, suggesting the 
idea (whence it derives its name) of a“ Table-Cloth.” Occa- 
sionally, when the wind is very violent, a ripple is formed 
on the erial current, which, by a sort of rebound in the 
hollow of the amphitheatre in which Capetown stands, is 
again thrown up, just over the edge of the sea, vertically 
over the jetty—where we have stood for hours watching a 
small white cloud in the zenith, a few acres in extent, in 
violent internal agitation (from the hurricanes of wind 
blowing through it), yet immovable as if fixed by some 
spell, the material ever changing, the form and aspect 
unvarying. The “Table-Cloth ” is formed also at the com- 
‘mencement of a “north-wester,” but its fringes then 
descend on the opposite side of the mountain, which is no 
less precipitous.’ 
Other illustrations, perhaps more pertinent, are supplied 
by sand ripples on the shore, and by the contour of sand 
drifts, while an illustration of reboundings out at sea, 
like to the ewrial rebound described in the passage cited 
from the writings of Sir John Herschel, are supplied by 
banks in some of the Argyleshire lochs, which, vertical to 
