The south dips of this basin range from 30° to 35°, and the north dips about 70°. It would thus appear that even this basin has been changed from its normal condition ; because we cannot conceive how sedimentary strata could form at an angle so steep as 70°. It seems to be an impossi bility. However the coal may have been formed, the overlying strata must have been deposited as sediment in water. This sediment would not be deposited uniformly in basins having high angles of dip, but would accumulate much more rapidly in the bottom of the basin than on its steep sides, particularly if they dipped at an angle of 45° or over. Therefore, as we find but little difference between the thickness of the strata at right angles on steep and even inverted dips and that of the horizontal strata, we conclude that most of the anthracite basins have been contracted, depressed, or elevated, and that their angles of dip have been greatly increased. Where the strata are contorted, we almost invariably find the coal crushed and powdered ; but where we do not find evidence of violent contractions, or where the coal has not been subjected to a crushing process, the seams are not injured in this respect. "Faults," however, are common
in all formations; but they are less frequent in well-defined planes and in smooth and regular strata than in twisted, knotty, and rippled sediment : these irregularities are primal faults, and not the effects of subsequent causes. Coal, however, may be changed by other causes than the influ ences of contraction, and to the irregularities in coal formations, due to such subsequent causes as slips, "up-throws," "down-throws," "crushed strata," inverted measures, &c., we may add those caused by heat, trap dikes, and like phenomena, which have also changed the normal condition of coal by exhausting its carbon and dividing and distorting its strata. "Primal faults" are the effects of original causes. These causes we will not attempt to explain in this connection, but will offer instances and their inferences in a future chapter, under the head of "faults and irregularities :" —we allude to "rock faults," "dirt faults," " slate faults," "bottom and top rolls," &c. &c.