The district between the mountain and the narrows, the thickly settled and well-cultivated plain bordering Amboy bay, and much of the western division of the island, are decidedly alluvial. Adjacent to Fort Tompkins, detached pieces of copper ore have been found. I have observed petrifactions of marine shells in rocks excavated in that neighbourhood, twenty feet from the surface, and sixty above the ocean. The western part of the island presents moderate elevations; the soil, a good medium of sand and clay, is in general fertile; but a tract near the termination is sandy and barren. Some creeks penetrate to near the centre of the island, and are bordered by extensive salt meadows. Except at the primitive range, I have observed in no part of the island large beds of rock that can be called in place; but rolled masses of greenstone, sandstone, gneiss, granite, red jasper, and indurated clay, appear in general sparingly, but sometimes in abundance, on the surface. Lignite has been found in small quantities in the western part of the island. A chalybeate spring, of no great strength, is the only mineral water met with in Richmond county. The ponds, wells, and streams, contain a soft water, holding no lime in solution. REMARKS. We have already published (p. 54.) Mr. Pierce's discovery of the pulverulent carbonate of magnesia, and have pointed out its connexion with Dr. Bruce's previous discovery of the hydrate of magnesia, or pure magnesia combined with water only. Mr. Pierce has now added another important link to this chain, and future mineralogists may quote the vicinity of New-York as affording, 1. Pure magnesia, crystallized and combined with water only. 2. Carbonate of magnesia, pulverulent and white. 3. Carbonate of magnesia, in very delicate and perfectly white acicular crystals. We possess specimens of them all. ART. X. _On a curious substance which accompanies the native Nitre of Kentucky and of Africa. Communicated in a letter to the Editor, from_ SAMUEL BROWN, M. D. _late of Kentucky, now of the Alabama Territory_. REMARKS. The scientific public were several years ago laid under obligations to Dr. Brown, for a very interesting and instructive account of the nitre caverns, &c. of Kentucky, published in the Transactions of the Philosophical Society, in Philadelphia, Vol. VI., and in Bruce's Journal, Vol. I. p. 100. The following communication arose from a conversation on that subject between Dr. Brown and the Editor. _New-Haven, July 27, 1818._ DEAR SIR,