In working this great quarry of anthracite at the Summit mine, above Mauch Chunk, blocks of coal were occasionally left standing for a time, one of which, surmounted by the soil of the original surface and the relics of the vegetation, is represented in the above cut. In this block are discerned the lines of stratification of the coal; and an idea of its extraordinary thickness and extent is conveyed by the appearance of the cliffs upon the further side of the excavated area. Upon the floor of the quarry are seen the mining wagons used for conveying away upon temporary tracks the coal and rubbish of the excavations.

whole area of this field has been computed at 57,000 square miles; but its limits have never been accurately defined. A fourth coal-field occupies the central portion of the southern peninsula of Michigan, its area being about 13,350 square miles. Several small beds of bituminous coal are worked in this district, but they have only local importance. A fifth coal-field is that of Rhode Island and south-eastern Massachusetts. The strata of this district are considered as belonging to the true coal-measures, although, from the metamorphic action to which they have been subjected, their true character is very obscure. They contain a few beds of anthracite, very irregular in their dimensions, and much crushed. A number of thickness have been opened, and worked to mines have been opened, but the only one now worked is at Portsmouth, 8 miles north of Newport. In south-eastern Virginia is a bituminous coal-field, lying on both sides of the James River, a few miles above Richmond. The strata which contain the coal-beds of this district are recognized as members of later formation than those of the true coal-measures, being classed with the geological group known as the oolite, or lias; and the coal-beds of central North Carolina, on Deep River, probably belong to the same position in the geological column. Notwithstanding the limited area of this coal-field in Virginia, which is only about 25 miles long and 8 to 10 miles wide, it has produced for more than sixty years past large quantities of coal chiefly for the supply of iron manufacturing establishments, and the gasworks along the seaboard to the north. The strata of these coal-measures occupy a deep depression in the granitic rocks of this region, attaining in the centre of the basin a thickness of nearly 2000 feet. They consist in great part of a micaceous sandstone, and the two or three coal-beds are contained in the lower 150 feet. A great bed at the bottom, which in some places exceeds 40 feet in thickness, and in others dwindles away to 4 or 5 feet only, appears to have been deposited upon the uneven granitic floor, from which it is separated by only a few inches of slate. Shafts have been sunk near the east border of the coal-field to the depth of nearly 900 feet. The amount of coal obtained of late years does not probably exceed 130,000 tons per annum. A singular phenomenon is observed at one point in this district, where a coal-bed is penetrated and overlaid by a body of trap

rock. The coal near this rock is converted into a mass of coke, resembling that artificially produced, except that it is more compact and of a duller lustre.

A large amount of bituminous coal has been brought to Boston and New York, for many years past, from a coal field belonging to the true coal-measures, in Nova Scotia and Cape Breton. The same formation extends into New Brunswick, and ranges along the western part of Newfoundland, and has been estimated as comprising in all an area of 9000 square miles. The productive portions, however, are limited to a few localities upon the coast of Nova Scotia and Cape Breton, and at these, beds of great

the depth of from 200 to 450 feet. At the Pictou mines, opposite the southern point of Prince Edward's Island, one bed is 29 feet thick. Another bed, at the Albion mines, 84 miles from Pictou, affords 24 feet of good coal, and 12 more of inferior quality; and in Sydney, Cape Breton, are beds of 11 feet, 9 feet, and 6 feet, besides at least 11 others of less thickness. At the South Joggins cliffs, in Nova Scotia, the total thickness of all the strata of the coal-measures was found by Mr. Logan to amount to 14,571 feet, very much exceeding the thickness of the formation as observed in other places on the American continent.

The strata which make up the coal formation, the principal varieties of which have already been named, are regularly laid one upon another in no particular order, and amount in aggregate thickness to several thousand feet, rarely exceeding in the United States 3000 feet. Their thickness is ascertained by sections measured at different localities, some giving one part of the column, and others other portions. In western Pennsylvania the nearly horizontal beds of rock are often exposed in the sides of the precipitous hills, so that sections of several hundred feet may be fully made up. Any peculiar member of the pile, as a bed of limestone, occurring near the top of the section, may be recognized in other localities, where by the dip of the strata it is brought to the lower levels, and the hills above it then present the succession of the higher members of the column; or if the layer taken as the starting point be in the one case at the base, it will be found in the direction of the rising of the strata, at higher and higher elevations, and the lower mem

continent itself, and have not been subjected to any local disturbences, such as in other regions have disarranged and metamorphosed the strata.

bers of the column will then be brought around the margins of the coal-fields and into view at the base of the hills. Thus, at define their limits. At Pittsburg this Pittsburg, the hills opposite the city afford group, it is found by boring, as well as by a section of 300 or 400 feet, and the marked the measurements of the strata in the hills stratum is here the great coal-bed, which up toward the north, is about 600 feet below the Alleghany river toward the north rises the level of the river. The coal-measures to higher and higher levels in the hills, and in this portion of the country are the hightoward the south, up the Monongahela, sinks est rock formation; but in the western territo lower levels, till it passes beneath the bed tories beyond the Mississippi they pass of the stream. By extending these obser- under later geological groups, as the cretavations over the coal-field, it is found that ceous and the tertiary. All the coals are the whole series of strata maintain their bituminous, and the strata in which they are general arrangement, and the principal mem- found are little moved from the horizontal bers of the group, such as an important coal-position in which they were originally debed, a peculiar bed of limestone, etc., may be posited. They have been uplifted with the identified over areas of thousands of square miles. It is thus the sections have been prepared at many localities to complete the series, as presented on the opposite page, of the bituminous coal-measures of the ex- East of the Alleghanies, in the narrow, treme western part of Pennsylvania. The elongated coal-fields of the anthracite recoal-beds introduced are those which are gion, a marked difference is perceived in the persistent over the greatest areas. Others position assumed by the strata, and also in occasionally appear in different parts of the the character of the individual beds. They column, and various other local differences evidently belong to the same geological semay be detected, owing to the irregularities ries as the bituminous coal-measures, and in the stratification; thus sandstones and the same succession of conglomerates, sandslates often thin out, and even gradually stones, and red shales, is recognized below pass from one into the other. By their them; but the strata have been tilted at vathinning out beds of coal separated by them rious angles from their original horizontal in one locality may come together in another, position, and the formation is broken up and and form one large bed; and again, large coal- distributed in a number of basins, or canalbeds may be split by hardly perceptible di- shaped troughs, separated from each other visional seams of slate or shale, which may by the lower rocks, which, rising to the gradually increase, till they become thick surface, form long narrow ridges outside of strata, separating what was one coal-bed and around each coal-field. Those on each into two or more. The limestones, though side being composed of the same rocks, simgenerally thin, maintain their peculiar char-ilarly arranged, and all having been subacters much better than the great beds of jected to similar denuding action, a striking sandstone or shale, and are consequently the best guides for designating in the columns the position of the strata which accompany them, above and below. The fire clay is almost universally the underlying stratum of the coal-beds. In the sections it is not distinguished from the shale-beds. The total thickness of all the measures, is from 2000 to 2500 feet.

Such is the general system of the coalbearing formation west of the Alleghanies. Every farm and every hill in the coalfield is likely to contain one or more beds of coal, of limestone, of good sandstone for building purposes, of fire clay, and some iron ore; and below the surface, the series is continued down to the group of conglomerates and sandstones, which come up

resemblance is observed, even on the map, in their outlines; and in the ridges themselves this is so remarkable that their shapes alone correctly suggest at once to those fa miliar with the geology of the country, the rocks of which they are composed. Upon the accompanying map, from the first vol. of the "New American Cyclopædia," these basins are represented by the shaded portions, and the long, narrow ridges which surround the basins, and meet in a sharp curve at their ends, are indicated by the groups of four parallel lines. Within the marginal hills the strata of the coal-measures, and of the underlying formations, while retaining their arrangement in parallel sheets, are raised upon their edges and thrown into undulating lines and sharp flexures; and the extrac