Physical geography. By Mary Somerville ...

CHAP. X. GEOLOGICAL NOTICE. 119
The plains are often unhealthy, but the air in the mountains is salubrious; fever has never prevailed at the elevation of 2500 feet.
Cuba, the largest island in the Colombian Archipelago, has an
area of 3615 square leagues, and 200 miles of coast, but so beset
with coral reefs, sandbanks, and rocks, that only a third of it is ac.
cessible. Its mountains, which attain the height of 8000 feet
occupy the centre, and fill the eastern part of the island, in a great
longitudinal line. No island in these seas is more important with
regard to situation and natural productions; and although much of
the low ground is swampy and unhealthy, there are vast savannahs,
and about a seventh part of the island is cultivated.
The Bahama Islands are the least valuable and least interesting
part of the Archipelago. The group consists of about 500 islands,
many of them mere rocks, lying east of Cuba and the coast of
Florida. Twelve are rather large, and are cultivated; and, though
arid, they produce Log-wood and Mahogany. The most intricate
labyrinth of shoals and reefs, chiefly of corals, madrepores, and
sand, encompass these islands; some of them rise to the surface,
and are adorned with groves of palm-trees. The Great Bahama is
the first part of the New World on which Columbus landed-the
next was Haiti, where his ashes rest.
The geology of Central America is little known; nevertheless it
appears, from the confused mixture of table-lands and mountainchains in all directions, that the subterraneous forces must have
acted more partially and irregularly than either in South or North
America. Granite, gneiss, and mica-slate form the substrata of the
country; but the abundance of igneous rocks bears witness to strong
volcanic action, both in ancient and in modern times, which still
maintains its activity in the volcanic groups of Guatemala and
Mexico.
From the identity of the fossil remains of extinct quadrupeds,
there is every reason to believe that the West Indian Archipelago
was once part of South America, and that the rugged and tortuous
isthmus of Central America, and the serpentine chain of islands
winding from Cumana to the peninsula of Florida, are but tile shattered remains of an unbroken continent. The powerful volcanic
action in Central America and Mexico, the volcanic nature of many
of the West Indian Islands, and the still-existing fire in St. Vincent's, together with the tremendous earthquakes to which the
whole region is subject, render it more than probable that the Carib.
bean Sea and the Gulf of Mexico are one great area of subsidence,
which possibly has been increased by the erosion of the Gulf-stream
and ground-swell-a temporary current of great impetuosity, common among the West Indian Islands from October to Mlay.
The subsidence of this extensive area must have been very great,,ince the water is of considerable depth between the islands. It