Page:The American Cyclopædia (1879) Volume I.djvu/627

 APPALACHIAN MOUNTAINS 591 mountains and metamorphosed the rocks of the most eastern ridges, are thrown into con- fused and intricate positions, and pressed into folds and wrinkles, the prevailing inclination of which is toward the southeast as hori- zontal layers of heavy cloth, pressed laterally by irresistible force from one end of the pile, would be lifted into folds, whose general in- clination, by the falling back of the arches, would be toward the direction where the force is applied. The direction of the line of force is that of the ridges themselves, or rather of the anticlinal and synclinal axes, the one being the crest of wave-like form into which the strata are thrown, and the other the trough. This, too, is the line of the great fissures, which, now filled with metallic ores, constitute the mineral veins of the chain. It is the line of the rents caused by the earthquakes of the present period ; and it is regarded by the Profs. Kogers as the line along which the elevating force that lifted the mountains extended, mov- ing onward at right angles to this line, with a wave-like motion, till the result was attained of placing the ridges in their present positions. Toward the southeast, whence the movement proceeded, the axes are crowded near to- gether. Toward the northwest they are re- peated at distances gradually increasing, till the undulations at last flatten out and die away in the horizontally stratified regions of the west. The straightness or regular curvature of these axes, and their parallelism in distinct groups, continued for distances sometimes amounting to over 100 m., without change in the stratification or topography, cannot fail to excite the astonishment of the geological ob- server. Among these axes are particularly noticed by the Profs. Eogers the straight axis of Montour's ridge in the Susquehanna region, which extends about 80 m. ; the beautifully inflected axis of Jack's mountain, in the Poto- mac region, 90 m. long ; and that of the Knob- ly mountain, nearly a continuation of the last named, itself 100 m. long. In S. W. Virginia, the straight axis of Clinch mountain is traced for more than 120 m. The strata of the Ap- palachian system are all of marine or ter- restrial origin. The fossils they contain are all of families belonging to the salt water, or plants of terrestrial growth. The latest or uppermost groups are those of the coal forma- tion. Throughout the whole chain none of the stratified rocks belong to a later epoch. Their elevation, then, must have taken place previously to those periods, when the upper secondary rocks, that lap upon the extreme eastern border of the Appalachian formations, were deposited, and previously to those still later periods when the great deposits of ter- tiary marls, sandstones, and clays were pro- duced, which cover the S. E. part of our country. These mountains are then of much older date than the Alps or the Andes, upon the high summits of both of which rest the rocks of these later formations, containing their characteristic marine fossils. Raised probably by many successive impulses exerted on the same lines (it may be after long inter- vals of rest), the rush of the retreating waters appears to have opened those gaps through the ridges, which constitute a peculiar and most interesting feature in the topography and scenery of these mountains, and which could not have been produced by the action of any existing streams. The same rush of waters, acting upon piles of strata of various degrees of hardness, and consequent capacities of re- sistance, impressed upon these the forms ap- propriate to these properties. This is seen in the sharp outline of single beds of sand- stone, which project from the sides of the hill, around which they outcrop ; and in the reced- ing of the profile of the mountain against the beds of softer shales and slates. It is seen on a grander scale in the peculiar forms which each of the rock formations gives to the hills or mountains it composes, and which enables one to recognize it wherever met with by a glance at the topography. The regular arrange- ment of the rock formations throughout all their foldings and undulations is rarely dis- turbed by any of those sudden breaks which are common in other countries, and which bring into contact, by the displacement of por- tions of the series, strata usually far separated from each other. These "faults," however, are met with in several of the states, but par- ticularly in S. W. Virginia, where they extend for about 100 m. in length, their course being the same as that of the anticlinal axes out of which they grow. They appear to have re- sulted from the lateral thrust toward the northwest of the folded piles of strata. They are observed, always beginning on the N. "W. side of the anticlinal axes, in tracing these along their course, the strata on this side be- coming steeper and steeper, till at last they are inverted, and dip toward the southeast. At this point the strata appear to have burst asun- der along the line of greatest curvature, and the S. E. portion to have been lifted up, bring- ing its lower strata against the higher mem- bers on the other side of the line of fracture. The depth of this dislocation, or the extent of the displacement, increases toward the centre of the line of fault ; and where the length of this line, as in the district under consideration, stretches along for 100 m. or more, it cannot appear disproportional that the vertical dis- placement should in its central portions amount to -$ of this distance; and that the lower groups of the Appalachian system, usually sep- arated by intervening strata of four or five miles in thickness, should be brought in con- tact, so that the edges of one series abut against the edges of the other. Thus the lower lime- stones of the great valley of Virginia are seen in Montgomery county, and thence westward along the line of the Virginia and Tennessee railroad, in vertical position, with the strata of the far more elevated series containing coal