The saline materials vary widely in character and constitution. They are, however, chiefly salts of soda, lime, potash, and magnesia. Sometimes they exist in the condition of chlorides, sometimes of carbonates, and sometimes of sulphates. The reactions from which they are derived are many, and it will be proper here to give only a few illustrations. A portion of the salts of magnesia and soda are derived from the decomposition, by atmospheric influences, of volcanic, granitic, and other crystalline rocks. Where these materials exist in the form of felspar, hornblende, and pyroxene, the great decomposing agent is water charged with the carbonic acid of the atmosphere, by the action of which soda, magnesia, and lime are, with inconceivable slowness, dissolved out of the constituents of these rocks. There is no stream, however pure it may apparently be, which does not carry more or less of chlorides and carbonates in solution. The sulphates are derived mainly from subterranean sources. In the Rocky Mountain Region, one of the most common forms of sulphate is found very abundantly in the rocks of the Carboniferous, Triassic, Cretaceous, and Tertiary Ages, in the forms of gypsum and selenite, which are sulphates of lime. Whenever waters containing carbonate of soda are filtered through strata containing these sulphates, a double decomposition takes place, by which carbonate of lime and sulphate of soda are formed. The carbonate of lime is very slightly soluble in water, while the sulphate of soda is highly so, and it is well known that waters emanating from the sedimentary rocks just spoken of are very frequently highly charged with it. Such, doubtless, is the origin of this mineral in the so called alkaline waters of the west, and of all the soluble minerals which pass under the name of alkali it is one of the most common. Carbonate of soda is also abundant in the soils. It is frequently found in the summer time, coating the surface of bottom lands which earlier in the season have been submerged by the augmented streams. Common salt (chloride of sodium) is even more abundant than the sulphate. It is well known, however, that many of the sedimentary rocks, particularly those of the Triassic and Jurassic Age, contain an abundance of it, and there are many localities in the west where a very fair article of common salt is obtained by the lixiviation of the detritus of the red Triassic rocks. Incrustations of these soluble saline materials occur most abundantly in the vicinity of the rivers and in the bottom lands. This may at first seem somewhat strange, but it is susceptible of a ready explanation. In order that these salts may accumulate at the surface, there must be going on continually a slow transmission of moisture from under ground upward, and since a continuous supply of water is more frequently found in the bottom lands than elsewhere, it follows that the conditions of these accumulations are here more frequently fulfilled.