_Dolomite_.--This mineral has been very common in this locality. It differs, perhaps, as I have before explained, from magnesite in containing lime besides magnesia, and from calc spar by the _vice versa_. Much of the magnesite in this serpentine contains more or less lime, and is consequently in places almost pure dolomite, although crystals are seldom to be found in this outcrop, it all occurring as veins about a half-inch thick and resembling somewhat the gurhofite of Staten Island, only that it is softer and less homogeneous in appearance. Its color is slightly tinged green, and specimens of it are not peculiarly unique, but perhaps worth removing. Its characteristics are: first, its burning to quicklime before the blowpipe, distinguishing it from pure magnesite; second, its slow effervescence in acids. Besides these, its specific gravity is 2.8, hardness, 8.5; from calcspar it cannot be distinguished except by chemical analysis, as the two species blend almost completely with every intermediate stage of composition into either calc spar, or, what occurs in this locality, aragonite, similar in composition to it, or dolomite. The color of the last, however, is generally darker, and it cleaves less readily into its crystalline form, which is similar to calc spar, and of which it is harder, 3.5 to 3 of calc spar. _Aragonite_.--This mineral, identical in composition with calc spar, but whose crystalline form is entirely different, occurs in this locality in veins hardly recognizable from the magnesite or dolomite, and running into dolomite. It is not abundant, and the veins are limited in extent; the only distinguishment it has from the dolomite, practically, is its fibrous structure, the fibers being brittle and very coarse. If examined with a powerful glass, they will be seen to be made up of modified long prisms. The specific gravity is over 2.9, hardness about 4, unless much weathered, when it becomes apparently less. There are some small veins at the north end of the walk, and in them excellent forms may be found by cutting into the veins.