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Under the lens, this mineral appears as a conglomerate of round globules of phosphate of lime, coated with a thin crust of oxide of iron and imbedded in a solid mass, which, in the darker specimens consists also of phosphate of lime.
The analysis below, made of samples of different colors, which I collected myself, will show, that this mineral, whilst it contains a uniformly high per centage of phosphoric acid, is in some parts of the island richer in phosphate of lime than in others, where the amount of phosphate of iron and alumina is larger than in the former.
The richest specimens being obtained from below the surface, demonstrate that it improves with the depth.
Again, there are some layers which have a bright rusty color, rough texture and are very friable. In these the globules are not so close together, and the mass in which they are imbedded is almost pure oxide of iron.
These exposed for thousands of years, as they undoubtedly have been, to the atmospheric action, rain, etc., became disintegrated and loose, have gradually filled the cavities of the limestone rock, and thus formed the soft deposit, with which the upper flat of the island, some one thousand acres, is covered.
From this loose mass the first shipments into the Baltimore market were made. It was introduced under the name of Navassa Guano as such it was known, until Dr. Campbell Morphit, in his treatise on the different Guanos, (see American Farmer, Vol. II, No. IV.) pronounced it for the first time to be a mineral phosphate. It is a more or less coarse powder, of a rusty color, and otherwise well enough known at present, as to need further description.
This deposit, of which about four to five thousand tons are dug and ready for shipment, is, as seen by the analysis, the must inferior found on the island, but, I am glad to say, it forms also the smaller portion to be worked. By a proper process, however, it can be improved, raised to 64–65 per cent. of phosphate of lime, and thus made marketable, if desired.
While speaking of this upperland, I cannot neglect to mention the existence of a number of caves there of various sizes, the bottoms of which are covered with a fine grayish looking substance, widely different in its character from the other de-
