# Memoir on the Island of Navassa (West Indies)/Description of the Island

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II.—Description of the Island.
Rising abruptly from the depth of the sea, without sand beach, the lower rocky bluff of the Island of Navassa stands conspicuous as a perpendicular wall. Its foot incessantly battered by the waves which have undermined in it a deep cut, several feet high, would necessarily tumble down if it was not protected against further erosion by a fringing reef of living corals, forming a breaker several feet wide, very distinct from the white limestone of the bluff by its dull red color, shining under the emerald green waves.
A man could easily walk around the whole Island, following the foot of the bluff on the flat top of this roof, if the sea did not break constantly over it, and roll at many points into deep recesses, where the air, compressed by the rush of the waves, soon dilates again, and blows off with great violence the water in a fine spray, covering the surface of the sea, for a distance of several yards, with a snowy foam.
Those "air holes" are important records for the history of the elevation of the Island.
On the summit of this first bluff, forming a terrace, vary-ing from a few chains to about half a mile in width, rises a second bluff, less abrupt. The rocks successively rolling down from its sides, have in some places formed a declivity of about 45°, when in other places its summit still stands nearly perpendicular. The top of this second bluff forms the summit of the Island where it is designated as the "Upper Flat," when the first terrace is called the "Lower Flat."
This upper summit is at the highest point 310 feet above the level of the sea, inclining from south-east to northwest. Heavily timbered by gum and palm trees, it is intersected by several reefs forming annular depressions filled by deposits of Phosphate of Lime, which I will describe hereafter.
Those reefs present a very rough surface; rugous, pointed and in many places seem to be long piles of rocks, broken and ​heaped by the action of the waves; when in other places they are solid, and form continuous undulations, varying much in direction but not in form, which has always a tendency to be ring-like. This annular disposition is the most remarkable at the north-western extremity of the Island, where the vegetation has been destroyed for the digging of the Phosphate; there the edges of the bluff towards the sea, and the reef traversing the summit assume the form of a basin depressed to-wards its centre, in the shape of ellipse, the great axis being about a mile long, and the small axis not quite half a mile.
The whole summit of the Island itself has a similar shape, the form of an atoll. All around it, the edges of the upper bluff are raised in the shape of an immense brim, followed at variable distance by a second elevation of the same character, inclosing between the two, a depression where the vegetation grows more luxuriantly between the irregular masses of limestone, with all its cavities filled by Phosphate of Lime.
Many caves or holes of different sizes are found on this upper summit of the Island, principally near those reefs that I have just described. The deepest that I visited was 45 feet deep perpendicularly, forming an irregular room of about 30 feet diameter. The bottom was covered by a deep deposit of Phosphate, probably carried down by the flow of the rains, and increasing rapidly. I base my supposition on the rapid increase of the deposits in those caves on the fact that although they present many stalactites, no stalagmites are found except in some crevices where the water drips down above the actual level of the Phosphate. Those crystallizations, although generally made of Carbonate of Lime as usual, sometimes present strips of Phosphate in their layers of successive deposition.
Except at the north point of the Island, where the bluff descends without interruption down to the sea, all this upper structure is encircled by the terrace or shore platform. The height of this terrace, from an elevation of only 15 to 20 feet above the level of the sea at its extremity west of North Point, rises at Lulu Bay, the shipping point of the Island, to 60 feet; at the south-eastern end to 65 feet; and on the north side forms a low rocky beach, in some places sloping down to the level of the sea, till it terminates against the north side of the cliff of North Point.
​The lithological character of this shore platform and of the top of the Island are similar. The edges above the sea also present the form of a brim; the surface is intersected by several reefs running with the same irregularity, and all the cavities in the masses of limestone are filled with the Phosphate of Lime.
The limestone is hard, compact, clinks under the hammer, and takes a polish like a secondary white marble.
Nevertheless, in breaking some of those hard masses, I found in the interior, in several instances, small blue specks of Phosphate of Iron, and more commonly nests of Phosphate of Lime. This intermixture of Carbonate and Phosphate of Lime is also found in the corals now built by the Zoophites; and I even found a mass of coral entirely made of Phosphate of Lime, a pseudomorph of the ordinary Carbonate of Lime of the corals. I found again a very interesting specimen of this intermixture of corals made of Carbonate and Phosphate of Lime, in the interior of a small sponge taken from the sea.
Everywhere on the two flats, and on the sides of the Island, are found on the surface of the limestone the forms of corals, mostly of the species astrœas and madreporas. I may say that at every place that I have examined, there is hardly a space of a few yards square where those marks are not found more or less obliterated, showing evidently the organic origin of the limestone. In breaking some pieces of limestone from the reefs, I found cavities filled with branches of coral. It is well to say that those marks of corals are not found on the rocks forming the brim of the upper and lower bluffs. There the limestone is smooth as if polished by the action of the waves.
It is important to remark here that the Island of Navassa having been, as it seems, upraised from the depth of the sea, without beach, no sand or debris of shells have been accumulated by the joint action of the winds and waves, to fill and cement the cavities existing between the branches or masses of coral rock. Those cavities which might be described by every word conveying the meaning of hollowness, run from the top to the bottom of the Island through the different strata, and the openings so left have become the recipients of the deposits of Phosphate of Lime.
​In masses of rock, of such confused shapes, the lines of stratification are, of course, very obscure; still they may be traced plainly enough in several places on the perpendicular wall of the shore platform, and of the summit, to show the successive formation of the different strata on the top of each other. The vertical cracks or fissures formed by the contraction of the rocks, under the constant heat of the tropics, are always more irregular in shape, and shorter than the lines of horizontal stratification, and by a careful observer cannot be mistaken.
This horizontal stratification, in places favorable for observation, seems to dip with an angle of a few degrees towards the centre of the Island.
Like all the limestones of coral origin, the Navassa rock is not abundant in fossils. I could only collect two pectens from the upper flat, and a bivalve found in breaking a mass of limestone in the diggings of the lower flat. I have submitted those fossils, and other specimens for determination, to Professor F. V. Hayden, of the University of Pennsylvania, and thankfully quote here his letter on the subject:
Dear Sir:—I have examined with some care the specimens which you left with me, from the Island of Navassa, W. I., and I find them all of recent origin, geologically speaking. They affirm to my mind what you expressed to me as your own conviction, that Navassa is one of those coral reefs which are still now in process of formation along the Florida Coast, and many portions of the West Indies. The corals and the shells, a chama and pectens, are all identical with species living in those seas at this time. The white limestone is very interesting as throwing light on the manner in which the old limestones of the Paleozoic ages grew to their enormous thickness and extent.
Yours respectfully, F. V. HAYDEN.
To Eug. Gaussoion, Esq., Baltimore, Md.