The Virgin Islands

Share |

Homepage

The Virgin Islands

Cinnamon Beach, Virgin Island National Park, St. John Photographic Print
Schwabel, Jim
12 in. x 16 in.
Buy at AllPosters.com
Framed Mounted

The Virgin Islands, excepting the outlying member, St. Croix, which surmounts a small bank of its own farther south, rise from the largest bank of the Lesser Antilles. It extends 80 miles eastward from Porto Rico with a breadth of 25 or 30 miles. The islands in this group are largely or wholly of volcanic origin and are now in a late mature stage of dissection; but some of them include also larger or smaller areas of deformed and greatly eroded stratified rocks, chiefly slates, which appear to underlie the volcanic rocks.

The group includes, besides a number of small islands and islets, four good-sized mountainous members. Two of these on the east are British: Tortola, ten by three miles, 1780 feet high, and Virgin Gorda, nine by from one to three miles, 1370 feet high, which apparently consists of several smaller islands united by sand reefs. Two others farther west are American: St. John, eight by four miles, 1277 feet high, and St. Thomas, eleven by three miles, 1550 feet high. Ten days of my journey were spent on or near the lastnamed island, and during that interval I was enabled to visit two near-by islands on the mine-sweeper Grebe, through the courtesy of Captain Henry H. Hough, U. S. Navy, Governor of the American group.

All the islands, including Culebra on the west but not Vieques still farther west--these two being of Spanish settlement and associated with Porto Rico-nor Anegada, a low limestone island far to the east, are rather compactly grouped in an area much smaller than that of the great bank, which must nevertheless be taken as indicating, perhaps with moderate enlargement, the original extent of a subsided land mass.

The reduction of the composite land mass from its original mountainous continuity to its present submountainous discontinuity must be ascribed in part to erosion, whereby much of even the most resistant structures were degraded to subdued forms, and whereby the less resistant structures must have been reduced to lowlands of small relief; but the reduction of the original area of the composite mass from almost as great an extent as that of the present bank to the small fraction of that extent seen in the existing islands must be due chiefly to submergence, whereby all the worn-down lowlands have been drowned and only the subdued eminences now survive.

The larger islands give abundant evidence of this submergence in their embayments; and the submergence must here, as in the case of other islands already described, be due to subsidence, because the valleys now entered by embayments are so manifestly more maturely broadened--and also because they are in some cases of greater rock-bottom depth--than can be accounted for by low-level erosion during the Glacial epochs.