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island. It covers 1,000 acres, of which about forty have been worked, yielding from forty to forty-five thousand tons of phosphate of lime.
The water close to the shore is very bold, twelve fathoms deep, excepting a point near the western extremity, where a coral reef shoots out to the westward about one hundred and fifty feet, on which the depth of water is but twenty-seven feet, with fifteen fathoms all around it. The greater part of Navassa is densely wooded by palm trees and shrubbery common to the tropics. Large flocks of sea birds of various kinds roost on the trees of the lower part of the island, but their excrements are hardly perceptible. The climate is perfectly healthy; sea breezes moderate the tropical heat, so that even white labor can be employed without injury to health.
The only unfavorable feature of Navassa is the entire absence of springs. All the water necessary is either obtained from rains saved in cisterns, or has to be obtained from the near islands or the States.
Geological Formation.
The great progress made of late years in the science of geology, has made us so well acquainted with all the rock formations, that it is now a comparatively easy matter to determine and classify the different strata and place them where they belong.
Among the many petrified shells covering the joints of the limestone, the best preserved are Pecten Personatus, (the inner side of them,) Gryphaea Virgula and Ammonites Striatulus, in every respect like those so frequently met with in the Jura system of Europe. The limestone of Navassa belongs therefore to the secondary formation. It is of white color, has an uneven, rough fracture, enclosing some round grains (oolites) and apparently a great many small shells that cannot now be classed.
This island was, at the time of its origin, under the level of the sea, where the stratas were successively deposed in a more or less horizontal position. After a stratum of the compact limestone had been formed, layers of phosphate of alumina, phosphate of lime and globular lime, alternately changing with another, settled on it, being followed again by a stratum
