high degree of flexure, while the neighboring regions are but little affected by this form of disturbance. It is true that low anticlinals and synclinals may and do occur almost everywhere, and that the distinction between these and extreme plication is one of degree most probably and not of kind: still the fact of localization is none the less true-just as it is true that some countries are mountainous and others are not, though hills occur everywhere. (2) Plications are an invariable concomitant of mountain forms. Sometimes the folds themselves form mountains and ridges: sometimes they lie upon the flanks of ranges which are composed of granite cores that seem to have risen up out of the depths and pushed the strata aside to find exit. Considerable variety in the forms of the folds is found among different mountain systems, and this might lead to question as to the identity of the forces and the modes of their application which produced them. But on the whole this identity will become apparent upon comparison, subject however to such qualifications only as would naturally arise from the original condition and magnitudes of the masses acted upon and the extent to which the action has been carried. The plications of the Alps may be illustrated by doubling a quire of card-boards, plunging the fold into a plastic mass and leaving the edges to protrude. In the Himalayas and portions of the Andes this structure is said to be repeated. In the Rocky Mountains on the other hand the most easterly ranges often have a single upturned edge of the strata leaning upon the granitic masses, and forming a fringe of foot hills with the surfaces of the strata sloping towards the plains, and their edges facing the mountains across an intervening valley. The local and meaningless name "hog-backs" has been given to them, and become current in the rapidly increasing geological literature relating to this region. There is almost an exception to this generalization in the country drained by the Colorado River. Here and also in the Great Basin the rocks are cut by great faults and uplifted thousands of feet in tables, with the strata nearly horizontal or tilted so that one side of a range shows the surface and the other the faulted edges of the strata. It has been shown by J. W. Powell that faults are, in some cases at least, the equivalents of certain forms of plication, and the exception may be apparent only. Yet it is apparent that some modifying condition was present of the mode in which the disturbing force was applied. The converse proposition

that plicated regions are mountainous-is not always true. (3) Plications occur in regions of maximum sedimentation. Geologists seem to have paid little attention to this general fact, though it must have been frequently observed. The term maximum sedimentation is used here with reference to large bodies of sediments accumulated with rapidity. Thus the strata of the Mississippi Valley and central Russia, of paleozoic age though of considerable thickness in the aggregate, required for their deposition an epoch as long as those of Great Britain and the Appalachians, which are ten or fifteen times as thick. The two lattér are intensely plicated, while the former are but little disturbed. The Alps, Jura, Urals—in brief, all the mountainous and plicated regions of Europe-the Himalayas, the known portions of the Andean region, the Rocky Mountain system from Denver to the Pacific, are all regions which are plicated and contain maximum strata. The reverse proposition is also true— that regions of minimum sedimentation are comparatively undisturbed. It might be objected that as the known portions of the earth are of small extent relatively to the whole, such generalizations must await a great expansion of knowledge before they are entitled to acceptance; and this objection is a very forcible one. Still our knowledge is sufficiently advanced, and the concordance within the limits of observation is sufficiently complete, to justify a provisional acceptance, subject to the modifications of future discoveries. (4) The epochs at which the plications commenced, were those during or immediately following the deposition of maximum sediments. It has frequently happened that a region has received deposits through a long series of epochs, like Great Britain in the paleozoic age, and also the Appalachians; but in such cases the plication has been continuous also, for a general non-conformity is found in the beds of the different epochs. This generalization, if it truly represents an order of facts, is of high importance, and worthy of more attention than it has received in such discussions; for it suggests at once the possibility, not to say the probability, that the relation is something more than a mere coincidence. The degree of truth which it contains may be ascertained with approximate certainty by a careful comparison of such facts as are settled relative to the ages or epochs of disturbance, and these Some, it is true, are doubtful, and some are unknown. As to those which have been fixed with reasonable certainty, the as

are many.

sertion is believed to be without exception. (5) In some plicated regions there may be observed a marked coincidence or general parallelism between the directions of the axes of flexure and the axes of maximum sedimentation. For example, in the Appalachians, the lines of maximum deposit are longer in a direction nearly parallel to the Atlantic coast, which is also the direction of all the axes of flexure. The same correspondence is presented in the Alps, the Jura, and the other European ranges which have been carefully studied. But whether the same relation exists elsewhere is as yet uncertain. In the Rocky Mountain region, so far as observation has hitherto reached, the thicker strata do not usually occur in elongated narrow belts having a uniform trend, but are broad and irregularly defined. But there is also less regularity in the plication and forms of disturbance than is found in the Appalachians. Our knowledge of this vast region being at present very fragmentary, it would be rash to venture upon a generalization.

Such being the features which plications present, we may proceed to inquire whether the hypothesis under discussion adequately explains their origin. It assumes that plicated regions occur along lines of weakness in the crust, and that the work of collapse has been expended there, but does it suggest any reason why those places where the strata lie thickest should become the weakest? or why the particular epoch of disturbance should coincide with or immediately. follow the epoch of deposit? Whatever may be the meaning of these correlations, it is quite certain that they are not accidental, and it cannot for one moment be admitted that such a gratuitous assumption as these supposed lines of weakness is any explanation of them at all.

The displacements which the strata have suffered are frequently extreme. Not only are they buckled up into great wave-like ridges, but are frequently inclined past the vertical, and are sometimes turned almost completely upside down. In New England and the Middle States the palæozoic strata are so extremely flexed and the folds so closely pressed together that they present in many localities nothing but a series of beds all dipping to the southeast at a high angle. Yet in spite of the extreme displacement there is no chaos. The different beds are not crushed into fragments nor disorganized, but preserve their relative positions as perfectly as when they were deposited. However vast the disturbing force must have been, we

may well wonder at the gentleness and ease with which they have been lifted up or let down. As if to remind us how destructive the force might have been, we find here and there a few acres which have unmistakably been subject to lateral thrusts in consequence of the sliding of a large mass down a steep incline, or some other local cause, and the strata have "gone into pi." This preservation of continuity would suggest to the investigator who might endeavor to apply mechanical principles to the problem, that the force which produced the movements was a minimum force—that is, a force having the smallest intensity which is capable of producing the movement. But this is demonstrably a system of forces acting upwards at the anticlinals and downwards at the synclinals. It is equally capable of demonstration that of all possible modes in which a force could be applied to produce a fold, the horizontal or tangential application would require the greatest intensity. It is the latter force which the contractional hypothesis supplies. It is difficult to admit that it could produce plications at all: the most probable result of it would be the annihilation of all traces of structure and stratification. This inference will be strengthened by recalling a well-known law of mechanics that tendencies to rupture ("moments of rupture") increase with the cubes of dimensions, while resistances to rupture ("moments of resistance") increase only with the squares. The masses under consideration are, collectively, of the extent of states and empires; the individuals are mountain ranges and valley bottoms, and their coherence in the presence of the forces which are adequate to move them becomes by virtue of the foregoing law a vanishing quantity. Such masses, under the action of the supposed force, would be the merest rubble, and quite incapable of preserving their integrity. The action has been frequently illustrated by subjecting a pile of paper to compression edgewise. A closer analogy would be presented if the paper were reduced to ashes or charcoal before applying the pressure. A better, though far from adequate one, may be found in the chaos produced in the Arctic regions when a great ice-floe is driven upon a rocky

coast.

When this article was commenced, it was intended to show that the contractional hypothesis is inconsistent with the present arrangement of mountain systems and the principal forms of mountain structure, and finally, that the figure of the earth itself, now known by geodetic measurement to be nearly, if not quite a nor

mal spheroid of revolution, could not be, what it is, if the hypothesis be true. But the objections already advanced, are considered so insuperable, that further discussion of it seems superfluous. It is best to leave it here, for if the foregoing objections are insufficient to destroy its claim to acceptance, further opposition would be factious. The task of opposing a theory which has no competitor, is not an agreeable one, and it is especially burdensome in the present instance. For, if the opposition be well founded, it leaves geologists without any explanation of the innumerable facts which they have accumulated at the expense of so much study and labor. The writer has no theory of his own to propose: believing that the true solution must be the work of a master mind, able to cope with the subject, both from the geological and physical side. Yet, with much diffidence and a consciousness of the great magnitude of the problem, an attempt will be made to set forth a few considerations of a simple character, which may possibly prove of some small service in suggesting certain limitations which must govern future inquiry. An attempt will also be made to indicate a few conditions, which any theory must conform to before it can claim even a conditional acceptance. C. E. DUTTON.

(To be Continued.)

E

LAVELEYE AND THE KATHEDERSOCIALISTEN.

MILE DE LAVELEYE, of Liege, is a man of the first merit among the European economists. His works, like those of his friend Cliffe Leslie, of Belfast, bristle with facts and valuable observations. His readers may agree with or may profoundly dissent from him, but they cannot but be better informed on some points after a careful study of any work from his pen. This is no slight praise for an economist; the representative books of this, the most practical of the sciences, are by no means rich in this direction. One might read Prof. Cairnes's or Prof. Fawcett's works for a lifetime, and know about as much at the end as at the beginning. A good memory might carry away from their works a great mass of suppositions and probabilities; but no knowledge of any facts not known to the readers of any respectable journal. It is true that this is not the fruit of any mere intellectual barrenness in the orthodox