Physical geography. By Mary Somerville ...

136 PHYSICAL GEOGRAPHY. CHAP. XII.
the Andes, the mean height of the whole of South America is 1130
feet. North America, whose mountain-chains are far inferior to
those in the southern part of the continent, has its mean elevation
increased by the table-land of Mexico, so that it has 750 feet of
mean height.
The mean elevation of the whole of the New World is 930 feet,
and of the continental masses of Europe and Asia above the level
of the sea, 1010 feet. Thus it appears that the internal action in
ancient times has been most powerful under Asia, somewhat less
under South America, considerably less under North America, and
least of all under Europe. In the course of ages changes will take
place in these results, on account both of the sudden and gradual
rise of the land in some parts of the earth, and its depression in
others. The continental masses of the north are the lowest portions
of our hemisphere, since the mean heights of Europe and North
America are 670 and 750 feet.'
So little is known of the bed of the ocean that no inference can
be drawn with regard to its heights and hollows, and what relation
its mean depth bears to the mean height of the land. From its
small influence on the gravitating force, La Place assumed it to be
about four miles.2 As the mean height of the continents is about
1000 feet, and their extent only about a fourth of that of the sea,
they might be easily submerged, were it not that, in consequence of
the sea being only one-fifth of the mean density of the earth, and
the earth itself increasing in density towards its centre, La Place
has proved that the stability of the equilibrium of the ocean can
By the mensuration and computation of Baron Humboldt and Mr. Pentland, the elevation of the highest peaks, and the mean heights of the Himalaya, of the Equatorial and Bolivian Andes and the Alps, are as follows:Peaks. Mean Height.
Himalaya........................................28,178............15,670
Andes between 5~ N. and 20 S. lat...........21,424............11,380
Eastern Cordillera I B etween io.........2100...... 15,250
Western Cordillera f and 150 S. lat..........22,350....... 14,900
Alps...................................................15,739............ 7,353
The Peak of Dhawalaghiri is 26,862 feet high, and the Kunchinginga in
Sikim 28,178. Captain Gerard gives 18,000 or 19,000 feet as the height
of the snow-line on the mountains in the middle of the Asiatic table-land,
and 30,000 feet as the absolute elevation of the Kuenlun, but Colonel Sabine
observes that the latter figures require confirmation, no direct measures of
the peaks of the Kuenlun having been ever executed.
a The greatest depth hitherto attained by soundings was six statute miles,
or about 10,500 yards, in the North Atlantic, by the American expedition
lately sent to ascertain the existence of the false Bermudas. [The deepest
soundings ever made prior to the experiment referred to, was 4000 fathoms
or 24,000 feet, by an officer of the British navy, but it was not considered
to be very satisfactory.] See official despatch of Lieut. Maury, in a Washngton paper of November 8, 1850.