rise or sink into the spaces between isolated gypsum-lenticules. 5. Gypseo-saliferous formations are generally of local extent in one direction or in both, indicating that they were accumulated in a restricted portion of the ocean.

The productive salt formations of the United States are three. The Salina group is the source of supply of brine and gypsum to Onondaga and Cayuga Counties, New York. The vast manufacture of the Empire State is based upon this supply. Only the northern rim of the basin or formation is known (Fig. 92). Its outcropping edge was deeply excavated by the agencies of the ice-period, and the excava

Fig. 92. Longitudinal section of the Onondaga Salt Basin (from Superintendent's Report for 1857), showing the ancient excavation of the outcrop of the Salina group, now filled with gravel and clay, and saturated by an exudation of brine from the old stump of the formation.

tion was filled with gravel. The overflow from the notched rim of the basin saturates the gravel, and thus forms a vast inland salt-marsh. The strongest brine settles to the bottom of this basin, and is reached by wells of the ordinary kind, and pumped out. It seems inevitable that a supply obtained under such geological circumstances must be liable to rapid exhaustion. The facts show that the strength

of the brine is gradually diminishing. The same formation affords brine and gypsum in the vicinity of the Grand River of Ontario, and rock-salt and strong brine at Goderich. It is worked for gypsum in the vicinity of Sandusky, Ohio. It underlies the whole of the lower peninsula of Michigan (Fig. 91) in the form of a vast basin, whose borders come to the surface at Milwaukee on the west, Mackinac on the north, the Grand River of Ontario on the east, and Sandusky on the southeast. This great salt basin has been penetrated, under the guidance of geology, at St. Clair and at Point aux Barques, and successful wells eleven hundred feet deep are now in operation. A new well is about to be put in operation at Mount Clemens, in Macomb County, and others are in progress at various points.

The next saliferous formation, in ascending order, is one which is peculiar to the lower peninsula of Michigan, and has hence been styled the "Michigan Salt Group." Its geological position is between the Marshall sandstone and the Mountain limestone. It underlies, like a great dish, nearly the whole of the peninsula. Its outcropping rim is marked by a circuit of salt springs. Filtration has leached out most of the brine into the underlying sandstones. The gypsum, however, mostly remains in the formation, and is extensively worked. The wells of East Saginaw and Saginaw City are supplied from this formation. As in the case of the Salina basin, this one is reached by deep borings over the most depressed portion (Fig. 91). These borings were originally undertaken as the result of a pure geological induction, and strong and copious brine. was obtained at the depth of about eight hundred feet. The first rock, even, was one hundred feet from the surface, and the whole thickness of the Coal-measures had to be crossed. I consider such successes ample vindication of the utility of geological science. The geological sur

vey, of which this was but one of the results, cost the state five thousand dollars. The discovery of brine in the Saginaw Valley has added two millions of dollars to the capital of the state.

The next conspicuous salt formation in ascending order is the Coal-measures. The reader who recalls the surface conditions under which the coal was formed will at once perceive that there must have been a great concentration of sea-water in the remote and somewhat isolated lagoons and marshes in which much of the materials of the coal formation were accumulated. It will be noticed, also, that the associated strata are here, as elsewhere, predominantly argillaceous. As the Coal-measures are universally underlaid by the great Conglomerate, this becomes the reservoir in which the saline solutions from the Coal-measures accumulate. The Conglomerate is the "salt-rock" of Ohio, West Virginia, and Northeastern Kentucky. It also underlies a large central area in the peninsula of Michigan, and thus constitutes the third great salt basin within the limits of that state, each underlying the same central area. The shallow wells at Bay City, Portsmouth, and the Lower Saginaw River generally, are supplied from the Conglomerate. The deeper ones at the same places are supplied from the next basin below. The gypsum is generally dissolved out of the Coal-measures, but in Western Iowa it still exists in vast quantities.

In Southern Kentucky, and Northern and Central Tennessee, brine is obtained by boring into the "Silicious group"-a local name for certain members of the Mountain limestone. I will not attempt to decide whether this brine proceeds from the Coal-measures or the False Coalmeasures, or has had an independent origin.

In Texas, Colorado, and Kansas, salt and gypsum are supplied in vast quantities from formations of Mesozoic

age, as in Europe. In some of the Gulf States, especially Alabama, tolerably strong brine is obtained by boring into the lower argillaceous and arenaceous strata of the Cretaceous system. On the island of Petite Anse, on the coast of Louisiana, nine miles south of New Iberia, is a remarkable deposite of rock-salt, till very recently the only one known to exist east of the Rocky Mountains. Underneath the soil of at least one hundred and forty-four acres of this island lies a solid bed of pure rock-salt, in which pits have been sunk to the depth of thirty-eight feet without reaching the bottom. The mass of this salt is below high water. It is overlaid by about nineteen feet of clay, gravel, sand, and surface soil. Not less than twenty-two million pounds of salt were removed from the island during the eleven months previous to April, 1863. The supply is probably inexhaustible. This extraordinary mass may occupy the site of an ancient bayou, the bottom of which has been elevated, while the contiguous shores have been either eroded or depressed, so that the land and water have exchanged places. It is the opinion of Dr. Goessman, however, that it is "a secondary deposite, resulting from the evaporations of brine-springs originating from beds of rock-salt in some older geological formation, and not a direct residuum from any sea.

* Report of the American Bureau of Mines, 1867. Hilgard has also made an examination of this deposite. Sci. and Arts, Jan., 1869, p. 77.)

Professor E. W. (See Amer. Jour.

CHAPTER XXVII.

METHOD IN THE GROWTH OF CONTINENTS.

How impressive the

OW impressive the unity of purpose with which Nature has pushed forward the consummation of her vast schemes! Ends have been foreshadowed through almost an eternity of years, while the all-directing Mind has steadily controlled the ministering forces, in the midst of millions of disturbing agencies, till the premeditated work has been accomplished. We witness in the plans of the Infinite Architect the same intelligent cohesion of parts as in a well-laid human scheme; and while the relations of certain events far transcend the scope of our reason, and the perfection of contrivance is immeasurably superior to that of human designs, we understand enough and measure enough to know that a philosophy which is at once human in its method and divine in its comprehension underlies the whole chain of natural events. There is a logical relationship of things established by God and recognizable by man, and the sequences of events are ofttimes so clear that even finite intelligence is able to penetrate the future and unveil plans existing only in the Infinite conception.

This ideal connection of the parts of the Creator's universe is, perhaps, best traced among organized beings, but I propose first to point out its existence in the history of inorganic nature. The infinitely diversified features of the earth's surface have been wrought out by the operation of a few principles working through ages in definite modes. We see that certain rocks bear the evidences of their sedimentary origin. We look about, and find sedimentary ac