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The Bays of St. Thomas
 Inner and Outer Brass Islands, St. Thomas Photographic Print 16 in. x 12 in. Buy at AllPosters.com Framed Mounted No island enforces this conclusion better than St. Thomas. The submergence of valleys on its southwestern coast, has produced open bays which still have a considerable inland reach, although their heads are now occupied by delta flats; and it has isolated several hilly spur ends. Botany Bay at the west end of the island is a beautiful reëntrant between advancing points; Magens or Great North Side, Bay near the middle of the northern coast is a highly picturesque feature when viewed either from the mountain crest above it or from the sea offshore.
In estimating the depth of submergence demanded by these bays, it should be borne in mind that the shore line to which they were originally drained did not lie close to the perimeter of the island as defined by its present headlands but lay 10 or 15 miles farther away in the neighborhood of the present bank margin; and that a down-slow of the draining streams must have been maintained along all that distance. The inferred rock-bottom depth of 200 or 300 feet at the bay mouths should therefore be increased by an additional 100 or 200 feet in estimating the change of by which the present embayment of the island was caused.
The absence of all indications of valleyin-valley erosion appeared to me to demonstrate that on St. Thomas, as on other islands, the embayment of the shore line was produced by a considerable measure of subsidence in Preglacial and Glacial time, so that, when the ocean was lowered in the Glacial epochs, the streams were simply extended along their former courses. Had the subsidence taken place at a much later date, the lowering of the ocean in the Glacial epochs should have been accompanied, as above intimated, by valley-in-valley erosion; that is by the incision of narrow young valleys in the floors of the previously excavated, broadly mature valleys; but no signs of such compound valleys were seen.
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