GENERAL FORM OF THE EASTERN PALzEOZOIC STRATA.
We must here briefly notice the general configuration of the Palteozoic strata on the Atlantic slopes, in order to present clearly the contraction and foliation of the coal-strata, in conformity with the formations in which they exist, and which will be found more extensively treated in Chapter III.
Most of the north-dipping strata in the Blue Ridge and parallel moun tain-ranges are either vertical or inverted, as shown in figure 74, in the south basins of the anthracite measures, exhibiting this peculiarity from the great mountain-chains down to the mere roll in the coal measures. In the anthracite regions, this system of inverted or elevated strata is more marked and peculiar north of the Great Valley limestone formation than south of it ; but farther south, in the mountains of Virginia and North Carolina, it embraces a wider range, and extends from the gneissic rocks to the coal measures of the Alleghanies. But there, as here, the undulations are more acute to the east than the west. On the New River, in Mont gomery and Pulaski counties in Virginia, as will be shown in our descrip tion of the New River coal-field, the north-dipping strata are inverted as much as they are at Pottsville, and at many intervening points the same inverted feature is manifest, clearly demonstrating the fact that the deep inverted basins increase to the east and diminish to the west, along the entire Appalachian chain of the Atlantic slopes from north to south. Figure 74, or the transverse section of the coal-basins from the Sharp Mountain to the Mine Hill in the vicinity of Pottsville, is a miniature section of the foliation from the Blue Ridge to the Alleghanies, and exhibits generally the progressive increase in the dip of the strata from west to east.
As stated in Chapter III., this peculiar feature of the eastern forma tions is due first to volcanic influences, and secondly to the forces of contraction. Volcanic vents on the long line of granite coasts first caused a subsidence or depression of the eastern marginal depth of the ancient Appalachian Sea (now containing the Palmozoic strata from the Blue Ridge to the Rocky Mountains), and formed the base or synclinal axis of the deep Southern basins; and subsequently the forces exerted by the contraction of the exterior portions of the earth's crust crushed those basins together in a lateral manner, as shown by figure 6 and explained in that connection.
We can readily comprehend that the sharp axes of highly inclining strata would be the weakest point under those lateral forces, on the same principle that a book folds or hinges on its back ; and since those weak points existed on the long line of sea-coast, or volcanic shores, from one end of the Appalachian chain to the other, they now constitute our inverted axes of formation, and disclose the fact that the contractions of the entire Appalachian basin, from the Blue Ridge to the Rocky Mountains, were concentrated here, or along the weakest line of the crust-formations.
In figure 74, as above stated, will be found a miniature representation of this general contraction, and the features of the foliation as it decreases from east to west; and in the local illustrations will be found simple repetitions in miniature of figure 74. These irregularities, therefore, become the rule instead of the exception, and constitute a vast system of highly foliated strata,—doubled almost as acutely as the folds of a map or a handkerchief, and frequently inverted or leaning to the "wrong side" of the axis.
Figure 75, illustrating the "Jugular" formation at Coalcastle, is perhaps as correct a representation as could be given of this inverted feature ill our geological formations. We can only account for it on the principle which we have advanced as governing and controlling all such formations, and as many of our practical geologists account for similar foliations in the Alps and elsewhere.
We have illustrated this feature of the anthracite coal measures pretty fully from local formations. Figure 54 represents two inverted basins at Shenandoah City, in the Mahanoy coal region. The engraving does not fully show the basins, but both north and south dips appear as south dips in the same basin. Figure 93 is a representation of foliated strata at Wiconisco, in the western end of the Lykens Valley fork of the First, or Southern, coal-field. It exhibits a new feature, not entirely peculiar, but one that is rarely developed in the coal measures. The inverted strata are here developed in reverse order, and the whole formation, including the conglomerate, is shown to be elevated instead of depressed, but bent and distorted, evincing the effects of lateral contraction in the most positive manner, since no other force could produce the same effects.
In other portions of this work we have made frequent allusions to these inverted formations, particularly in reference to the "Jugular overthrow" at Coalcastle, and promised to explain them fully. We think this promise has been fulfilled in connection with the illustrations as they appear in order, and the present reference to the same.
The engravings, however, explain themselves to the practical mind, and convey a better impression of the subject than can be obtained from the text, however carefully worded, without their assistance.
If we have stated the facts clearly, there can be no doubt left in regard to the mythical character of the great Jugular humbug; and not only will that matter be settled, but all inverted dips and irregular forma tions in the anthracite coal measures may be accounted for and understood on the same general principle.