REVIEWS. 
511 
of Wales, leaving as their sole memento in these warmer days, the charm- 
ing lakes and torrents so well known to the lovers of Cambria. Before, 
however, proceeding to these generalities, a lecture is devoted to the ex- 
planation of the nature of the two great classes of rocks, the Igneous and 
Aqueous, with the sub-class of Metamorphic rocks, which were changed 
after deposition by the sudden heat of liquid lava. The nature of denu- 
dation is also explained, and, in illustration of the enormous power of run- 
ning water, Professor Ramsay alludes to the Niagara falls ; thus, “ denuda- 
tion ” in the geological sense of the word means the stripping away of 
rocks from the surface by some agent, so as to expose other rocks beneath. 
Now, water running over the surface, wears away the ground over which 
it passes, and carries away detrital matter, such as pebbles, sand, and mud ; 
and if this goes on long enough, there is no reason why any amount of 
matter should not in time be removed. For instance, we have a notable 
case in North America of a very considerable result from denudation now 
being effected by the river Niagara, where, at the Falls, the river has cut 
a deep channel through the rocks about seven miles in length. The proofs 
are perfect that the Falls were once at the escarpment, which is at the 
lower end of what is now this long gorge ; that the river, falling over this 
ancient escarpment, by degrees wore for itself a channel backwards and 
backwards, about a hundred and sixty feet deep, through upper strata that 
form a great plateau. 
Probable calculations show, that to form this gorge a period of some- 
tiling “like ten thousand years has been employed.” The manner in 
which deposits of mud, clay, limestone, &c., have been formed, is carefully 
described. As an example of the immense amount of mineral matter 
which water may carry in solution from rocks, the springs near Bath are 
mentioned, which yield 181,440 gallons of water per day, holding in solution 
3402 lbs. of salts, equal to 420 tons per year ; a quantity sufficient, if com- 
pressed and solidified, to form a column 9 feet in diameter and 140 feet 
high. Rivers, too, contain exceedingly large quantities of mineral matters ; 
the Thames at Teddington carrying along in its waters an amount equal 
to 33,497 tons per annum. The second lecture is devoted to the geology 
of Scotland, the various phenomena of metamorphism, and the nature of 
the igneous rocks. The various strata forming the surface of England 
and Wales, and their peculiarities of structure, form the subject of the 
third lecture. A very interesting ideal section is given, from Wales 
through Gloucestershire to the Eocene beds of Hampshire ; and the bearing 
of the geological structure of the country along the line of section upon 
its scenery is described : the clays forming plains ; the limestone, hills with 
escarpments suddenly rising from the flat surface below, their faces being 
washed away by the geologist’s giant “ denudation.” 
Perhaps the most interesting lecture in the series is that in which 
Professor Ramsay describes, according to a view which he has lately 
advanced, the origin of the Scotch and Welsh lakes. For this purpose 
he takes us first to Switzerland. Here he shows us the snow-capped Alps, 
with their valleys each containing a great glacier. The glaciers are 
formed by the compression of snow, which accumulates in enormous 
masses on the mountain sides. Fresh ice is thus continually formed and 
