rent beds, lying close to each other, but separated by their layers of slate-clay. Its thickness is about twenty-seven feet.

To convey an idea of the regularity of these strata, we here give the names of a few of them, and the succession in which they occur, beginning with the lowest.

15 Coal, (main,)

29

10

8 Coal,

deposit

the inh Orig

cano;

16 Bituminous shale, 7

See "Origin of, and Searching for Coal."

Secondary Limestone. This is also called carboniferous, and mountain limestone. Its texture is compact, and not crystalline, like the primitive limestone before described. Its prevailing colors are gray, or yellowish white, but it is sometimes bluish or black. This formation is sometimes extensive, underlaying large districts, and rising into considerable mountains. The hills of this formation often present mural, or wall-like precipices, and rocky, uneven dales.

It is considered a more recent rock than transition limestone, and is often composed, almost entirely of marine shells, sometimes only slightly adhering together. It also contains the bones of animals, chiefly of extinct species, but sometimes of those now living, and which are never found in the transition class. It is often difficult, however, to distinguish this rock from transition limestone, into which it insensibly passes.

Rock Salt. Although this salt cannot properly be classed as a rock, yet as it forms considerable beds, and is, withal, an important article, it is proper to describe its geological bearings and associations.

of the

In its impure state, as it is raised from the mine, rock salt is in large solid masses, of a crystalline structure, with a reddish or bluish color. When pure, as it sometimes

it has volcani

stances and app

occurs in the mine, it is perfectly colorless and transparent, like the best flint glass.

as to pre formed i The

account

situations ration of when it

of their e

as receivi the Polish

table imp

But on

out any o

of light is

these form salt lakes,

as shells, Another,& the great that obtain

Rock salt is found at various depths below the surface. t Cheshire, in England, where vast quantities are raised, e first bed is one hundred and thirty feet deep, and sev ty-eight feet thick. This is separated from the next bed a stratum of clay-stone, thirty feet thick. The lower d has been penetrated one hundred and twenty feet, but s not been sunk through.

The principal known deposites of salt, are those of Carna, in Spain; those of Hungary, and Poland; that of ramania, in Asia; the extensive formations of Germany 1 Austria; those on each side of the Carpathian mounns, and those of South America.

According to the traveller Chardin, rock salt is so indant in Caramania, and the atmosphere so dry, that inhabitants sometimes build their houses of it.

Origin of Rock Salt. At Posa, in Castile, there is a osite of rock salt, within the crater of an extinct volo; and in the island of Sicily, there exists more or less the same mineral, in such situations as to indicate that as been formed by the evaporation of sea water, by canic heat. But if subterranean heat has in a few inces produced salt by evaporation, still the situation appearances of these formations generally, are such o preclude any rational supposition, that they have been ned in this manner.

'he most natural hypothesis that has been offered, to ount for the existence of this salt, especially in certain ations, is that which attributes it to the gradual evapo▪n of pools, or lakes of salt water left by the ocean, n it retired from the present continents, in consequence eir elevation. This theory, too, might be considered eceiving strong support from the fact, that in some of Polish mines, sea shells, the claws of crabs, and vegeimpressions have been found.

ut on the contrary, most salt mines are entirely with any organic, or other remains, by which any gleam ht is thrown upon the history of their origin. Were formations the solid matter, left by the desiccation of akes, we should suppose that fossil sea animals, as well ells, ought to be found everywhere, and in abundance. her, and still stronger objection to this hypothesis, is reat purity of subterranean salt, when compared with

btained her

ononation of son water

With the exception of foreign impurities, such as clay and sand, rock salt is nearly pure muriate of soda; while sea water, by evaporation produces muriate of magnesia, and sulphate of soda, besides muriate of soda. The mode in which rock salt is disposed in the earth, is also against the hypothesis of evaporation. That of Cheshire, instead of being in strata, is found in distinct concretions.

To these difficulties, it may be added, that the depth of sea water required to produce some of the larger masses of rock salt, must not only have been unfathomable, but incomprehensible. The salt hill of Cardona is 663 feet in height, and is solid muriate of soda. Now, according to the experiments of Dr. Marcet, 500 grains of salt water, yielded 21 1-2 grains of solid matter, of which 13.3 parts were muriate of soda. From 10,000 parts of sea water, Dr. Murray obtained 220 parts of common salt.

According to such data, if the salt of Cardona was formed in a lake, by evaporation, the water not only yielded pure muriate of soda, but must have been more than 27,000 feet, or more than five miles in depth.

Finally, this subject appears to be one of great difficulty, for although geologists have made the theory of these formations a matter of much interest and inquiry, no rational hypothesis concerning them has yet been proposed.

Cu

ani

Gypsum. Sulphate of Lime. This is known under the name of Plaster of Paris, and is so common as to need no description. This substance, like rock salt, is seldom found in extensive formations. It occurs both with primitive and secondary rocks, and, from the species of shells it sometimes contains, has been considered a fresh water formation. Beds of gypsum commonly alternate with those of marl and limestone.

The greatest deposite of gypsum described, is that of Paris, which extends about twenty leagues. At Montmatre, near Paris, two formations of this substance may be observed; the lower is composed of alternate beds of little thickness consisting of gypsum, often crystalline, alternating with lime and clay-marls. The upper formation is the most important and remarkable.

It is about

sixty-five feet thick, and, in some places, lies immediately under vegetable mould. This is especially interesting, from the number and variety of organic relics it contains, and from its being the chief source whence the celebrated

tion.

avier drew the skeletons of so many extinct species of imals.-See Organic Remains.

Chalk. In England, chalk is a very important forman, both on account of its extent and its perfectly disctive characters. It is also found in France, Ireland, ain, Germany, Italy, and Poland; but it is a singular t, that no deposites of chalk have been found beyond the its of Europe. In the New World, through the whole ent of the two Americas, not a specimen of chalk has en found.

The chemical properties of chalk are those of carbonof lime, viz., lime 56; carbonic acid 44-100. When ll burned, chalk is said to make as good quick-lime as hardest marble. In the Isle of Wight, the harder ds are employed as building stones; and, at Dover, alk is used in the construction of docks, or other mary, which is covered by the water. Some very ancient ldings are constructed of this material, and among them abbey of St. Omar, in France, which is said still to in all its beautiful Gothic ornaments in great perfec

1.

With respect to the antiquity of chalk, it is considered a e recent formation than coal, and between it and the ary, or newer secondary formations.

eds of chalk generally contain nodules of flint and oric remains, especially those of shells, sponge, star-fish, repores, &c.; but some beds are entirely without flints. ntries underlaid with chalk are generally far from g flat or level, but, on the contrary, are remarkable heir undulations of surface, the hills having smooth ded outlines, with deep indentations, or hollows, in ⚫ sides.

hickness of Chalk Beds. Chalk beds vary in thickfrom a few inches to 1000 feet or more. At Dover, beds containing flints are about 500 feet thick, and › without flints 140 feet thick. At Culver cliff, in the of Wight, where these beds are disposed vertically, where Mr. Coneybeare says there is the best oppor7 afforded to ascertain their thickness, this has been about 1300 feet. But, generally, this formation in

Oolite. This is also called Roestone, Decause it is composed of small globules resembling the roe of fishes. It has generally a yellowish brown, or ochery color. It is a variety of common limestone, from which it does not differ in composition. These globules do not, however, in all cases, compose the entire mass; sometimes they appear to be imbedded in solid limestone, and, in other instances, they are wanting entirely.

In England, this formation is superincumbent on chalk, and often contains shells and other organic remains. It is employed as a building stone. St. Paul's church and Somerset house being constructed of this material. It is, however, said not to be a durable stone.

With respect to the manner in which these globules were formed, Mr. Bakewell remarks, that it is not yet ascertained whether they have resulted from a tendency to crystalline arrangement, or whether they are of animal origin. We should think neither would account for them; but that they were formed in springs, or rather running water, containing lime, by a gradual deposition of carbonaceous particles on a small nucleus, as a grain of sand, kept in agitation by the stream.

Lias. This name is said to be a corruption of the word layers, because this rock is usually stratified. It is one of the Oolitic group, and passes by insensible shades into Oolite. It is an argillaceous limestone, usually found in the conformable position. It retains a uniform mineralogical character throughout a great portion of England, France, and Germany. It is often rich in organic remains, and especially of the saurian reptiles.

In this country it is described by Dr. Hildreth as existing on the Little Muskingum, in Ohio. Color yellowish white when exposed to the air, but grayish white when taken from the bed; structure compact, fracture conchoidal, with an earthy surface; adheres to the tongue; composition, carbonate of lime, with a little carburet of iron. In properties and appearance it approaches nearly to chalk.

Dr. Hildreth says, "that it stands the weather without exfoliation, and would make a most beautiful building stone."

The associations of this rock, in Ohio, will be seen by the diagram, fig. 20.