Prospective Value of Salt Lake.A member of the geological survey says that Salt Lake will be of great value in the near future, not only on account of the common salt it will produce. but also for the sodium sulphate It eontains. The latter is separated in a flocculunt precipitate by the cold weather of midwinter and annually thrown up on the shore in enormous quantities. There are many other lakes in the far west whence an inexhaustible supply of commercial alkalies may bo obtained at small cost. Mono Lake. California, alone being estimated toht.lil nvor million liini ot