Graphite or plumbago, commonly but improperly called black lead, occurs extensively in primitive and transition rocks; from that which is obtained in New York, excellent pencils have been made. There are also numerous localities of petroleum, or mineral oil. It usually floats on the surface of springs, which in many cases are known to be in the vicinity of coal. It is sometimes called Seneca or Gennessee oil. In Kentucky, it occurs on a spring of water in a state sufficiently liquid to burn in a lamp; it is collected in considerable quantities. Salt appears to be abundant in the United States, but it has not been found in the mass. It is principally obtained from the springs which have been noticed in another part of the work. Professor Eaton has suggested doubts whether masses of salt really exist. He conceives that an apparatus for the spontaneous manufacture of salt may be found within the bosom of the earth, in those rocks which contain the necessary elements, and in this opinion he is supported by experiment. Subsequently, however, Mr. Eaton had reason to think that salt has existed in a solid state in cubical crystals, the hollow forms of which he discovered abundantly in the lias and saline rocks of the west, and it seems still to be highly probable that masses of salt exist in the neighborhood of the salt springs. The brine contains, besides the muriate of soda, a considerable proportion of muriate of lime and magnesia. Recently, also, bromine has been detected in the brine of salina, by Dr. Silliman. Saltpetre is abundant in the west, being found in numberless caves along the Missouri; and the shores of the Arkansas are almost covered with nitre. The testimony of Mr. Schoolcraft, in relation to the recent formation of quartz crystals, is very striking. They have been found, it appears, upon the handle of a spade, and the edge of some old shoes, which had been left for some years in an abandoned lead mine of the Shawnee Mountains. Crystals of great beauty and dimensions have been found in numerous localities. Many minerals which are rare in Europe, are found abundantly, and often in finer forms, in the United States; some, which have subsequently been detected elsewhere, were first discovered here, and not a few may still be claimed as the peculiar treasure of our country. GENERAL REMARKS ON MINERALS.