"On our return" [from the base of the Fall, and walking along the water's edge, under the cliff], "we employed ourselves in picking up a kind of stone, which is said to be the Spray of the Fall, petrified, but whether it is or no, I will not pretend to determine; this much I can say, that it grows, or forms itself in cavities in the cliff, about half way to the top, from whence it falls from time to time; its composition is a good deal like a piece of white marble which has been burnt in the fire, so that it may be pulverized with ease. Whatever may be its composition, it does not appear that it will bear to be exposed to the air, as some pieces which seem to have fallen longer than the rest are quite soft; while such as had lately fallen are of a much harder nature." Robert McCauslin, M.D., who, during and after the War of the Revolution, spent nine years at Niagara--undoubtedly as British Post Surgeon at Fort Niagara,--furnished a scientific paper entitled, "An account of an earthly substance, found near the Falls of Niagara, and vulgarly called the Spray of the Falls," to Dr. Benjamin Smith Barton; and he, on October 16, 1789, communicated it to the American Philosophical Society; in whose Transactions it was subsequently published. Dr. McCauslin specially noted, that "This substance is found, in great plenty, everywhere about the bottom of the Falls; sometimes lying loose among the stones on the beach, and sometimes adhering to the rocks, or appearing between the layers upon breaking them. The masses are of various sizes and shapes, but seldom exceed the bulk of a man's hand. Sometimes they are of a soft substance and crumble like damp sugar; while other pieces are found quite hard, and of a shining, foliated appearance; or else opaque and resembling a piece of burnt allum. It often happens that both these forms are found in the same mass. Pieces which are taken up whilst soft soon become hard by keeping; and they are never known to continue long in a soft state, as far as I have been able to learn." He records that it is not found at all above the Falls, in the greatest amounts in the Gorge, close to the Falls; and in decreasing quantities as the distance from them increases; and is never found at a greater distance from them than perhaps a mile. From several scientific experiments which he made upon this substance, he deduced, "1st, That this concrete is not an alkaline earth, as it is not affected either by the vitriolic or vegetable acids. "2d, That we may, with more probability, say that it is a combination of an acid with a calcareous earth, and that it might with propriety be ranked amongst the selenites."