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The Composite Island of St. Croix Little attention has been thus far paid to the work of earlier observers, because they have as a rule given only secondary consideration to the structural and physiographic features of the Lesser Antilles, upon which the discussion presented in the foregoing pages has been largely based. But if we now turn to examples of second-cycle composite islands, geological structure becomes of large importance, as it was in the case of the second-cycle simple island of Sombrero, already described, and the reports of geologists who have examined such islands must therefore be taken into account. St. Croix, the southernmost of the Virgin Islands but separated from them and their great bank by a broad passage of deep water, is five miles wide at its western end, whence it narrows in its 17 miles of length to a slender point at the eastern end. It surmounts a bank, two or three miles wide off the southern shore, and extending ten miles east of the island with a breadth of four or five miles. I saw a good part of the island during an active visit of a day and a half, when Mr. Lindborg, director of education, and Mr. Gebhardt, government engineer, were so good as to drive me about in their cars. The structure of the island has been well described by Quin, a local observer, from whose very serviceable book26 many of the following details are taken. The fundamental rocks are slates and shales, many thousand feet in total thickness, strongly deformed, cut by dikes, and deeply eroded by insequent streams. These rocks form a maturely dissected mountain mass occupying a small quarter of the island along the western third of the northern coast-a part of their descent near the northwestern corner of the island being very precipitous--and a range of subdued hills occupying the narrowing eastern halflength of the island. A body of calcareous strata, mostly thin-bedded limestones, over 600 feet thick and dipping gently southward, occupy the southwestern half of the island and rest unconformably on the fundamental rocks; but the general form of the surface of contact has not been described. The calcareous beds are described by Vaughan as of midTertiary date. 27 The uppermost members have been largely worn away, so that the present surface includes a low and discontinuous cuesta on the south and a beveled lowland, largely occupied by sugar plantations, farther inland; the lowland rises gradually toward the mountains on the northwest and the hills on the east. According to Quin it extends between the mountains and the hills nearly to the northern coast, there rising to a considerable altitude a short distance next west of the middle point and then falling rapidly to the shore. In their initial form these calcareous beds probably covered a good part of the eastern hills and lapped much higher than now on the northwestern mountains, possibly covering their tops. Before the uplift of St. Croix, whereby its limestones were exposed to erosion, it is believed that they had been accumulated on a reef-enclosed lagoon floor, from which a part of the northwestern mountains and perhaps some of the eastern hills rose as islands. That this condition was the result of slow sinking is clearly shown by the manner in which the limestones unconformably overlap the eroded surface of the older rocks. Hence, although those rocks are not volcanic, the first-cycle history that they and the limestones record is again that of aggradation during subsidence. That a barrier reef rose around the outer border of the area on which the limestones were accumulated is made probable by the absence of all signs of wave-cut cliffs on the southern slopes of the northwestern mountains where the limestones approach them. Before the first cycle in the history of St. Croix was interrupted by uplift, the old-rock islands appear to have been reduced by submergence to so small an area that the encircling reef might have been almost or truly an atoll. If the precipitous part of the northern slope of the northwestern mountains was then as steep as it is now, the reef must have been attached to it as a fringe; just as the great barrier reef of Tagula, east of New Guinea, is attached to a part of the northern coast of that island as a fringe, although it is elsewhere a barrier enclosing a great lagoon over 100 miles in longer diameter. It has been suggested, however, that the precipitous part of the northern coast is a fault scarp produced when the second cycle of island history was introduced by uplift; but with that possibility we are not here particularly concerned. In consequence of the uplift of the St. Croix almost-atoll, probably accompanied by a slight tilting to the south as the limestones are gently inclined in that direction, the reduced old-rock islands have regained some of their previously lost height and, in consequence of the erosion of their limestone cover since uplift, some of their previously buried extension. The limestone area has at the same time been degraded to a beveled inner lowland enclosed by a weak and discontinuous cuesta, as above stated; and the inferred almost-atoll reef has been, in so far as it was elevated, destroyed either by normal erosion or by low-level abrasion or by both. Singularly enough, the shores of the present island are little embayed and are not cliffed, with the exception of the precipitous part of the northern slope of the northwestern mountains and of little nips cut at present sea level in sloping headlands east of that part. This makes St. Croix unlike the islands thus far described. The absence of shore cliffs along the western end of the island where Frederiksted stands on an open coast near the junction of the limestone cover with its founation rocks was very striking. Cliffs are again wanting along the northern side of the eastern hills where Christiansted, the chief town of the island, has a reef-enclosed but shallow harbor and farther east, and also along the low exterior slope of the weak cuesta of the southwestern limestone area. The absence of cliffs on this island constitutes an unexplained failure of the Glacial abrasional element in the scheme of Lesser Antillean development; perhaps it may be ascribed to a better persistence of reef protection in the Glacial epochs here than elsewhere. Unexplained also is the unusually small depth of the present bank; it is generally less than 17 fathoms over the greater part of its surface, and seldom more than 20 fathoms at its outer border: like the absence of embayments, this suggests recent uplift. Discontinuous fringing reefs rise at various points near the island shores, and some submerged bank-barrier reefs, with depths of 6 or 8 fathoms, are charted on the southeastern part of the bank. Home