BEFORE entering upon a sketch of the growth of the European Continent from the earliest times until it reached its present dimensions and outlines, I will say something of the growth of continents in general, connecting these remarks with a few words of explanation respecting some geological terms, which, although in constant use, are nevertheless not clearly defined. I will explain, at the outset, the meaning I attach to them and the sense in which I use them, that there may be no misunderstanding between me and my readers on this point. The words Age, Epoch, Period, Formation, may be found on almost every page of any medern work on geology; but if we sift the matter carefully, we shall find that there is a great uncertainty as to the significance of these terms, and that scarcely any two geologists use them in the same sense. Indeed, I shall not be held blameless in this respect myself; for, on looking over preceding articles, I find that I have, from old habit, used somewhat indiscriminately names which should have a perfectly definite and invariable meaning.

As long as zoological nomenclature was uncontrolled by any principle, the same vagueness and indecision prevailed here also. The words Genus, Order, Class, as well as those applied to the most comprehensive division of all in the animal kingdom, the primary branches or types, were used indiscriminately, and often allowed to include under one name animals differing essentially in their structural character. It is only since it has been found that all these groups are susceptible of limitation, according to distinct categories of structure, that our nomenclature has assumed a more precise and definite significance. Even now there is still some inconsistency among zoologists as to the use of special terms, arising from their individual differences in appreciating structural features; but I believe it to be, nevertheless, true, that genera, orders, classes, etc., are not merely larger or smaller groups of the same kind, but are really based upon distinct categories of structure. As soon as such a principle is admitted in geology, and investigators recognize certain physical and organic

conditions, more or less general in their action, as characteristic of all those chapters in geological history designated as Ages, Epochs, Periods, Formations, etc., all vagueness will vanish from the scientific nomenclature of this department also, and there will be no hesitation as to the use of words for which we shall then have a positive, definite meaning.

Although the fivefold division of Werner, by which he separated the rocks into Primitive, Transition, Secondary, Alluvial, and Volcanic, proved to be based on a partial misapprehension of the nature of the earth-crust, yet it led to their subsequent division into the three great groups now known as the Primary, or Paleozoic, as they are sometimes called, because here are found the first organic remains, the Secondary, and the Tertiary. I have said in a previous article that the general unity of character prevailing throughout these three divisions, so that, taken from the broadest point of view, each one seems a unit in time, justifies the application to them of that term, Age, by which we distinguish in human history those periods marked throughout by one prevailing tendency;-as we say the age of Egyptian or Greek or Roman civilization, the age of stone or iron or bronze. I believe that this division of geological history into these great sections or chapters is founded upon a recognition of the general features by which they are characterized.

Passing over the time when the first stratified deposits were accumulated under a universal ocean in which neither animals nor plants existed, there was an age in the physical history of the world when the lands consisted of low islands, - when neither great depths nor lofty heights diversified the surface of the earth,-when both the animal and vegetable creation, however numerous, was inferior to the later ones, and comparatively uniform in character, when marine Cryptogams were the highest plants, and Fishes were the highest animals. And this broad statement holds good for the whole of that time, even though it was

There was an age in the physical history of the world when the patches of land already raised above the water became so united as to form large islands; and though the aspect of the earth retained its insular character, yet the size of the islands, their tendency to coalesce by the addition of constantly increasing deposits, and thus to spread into wider expanses of dry land, marked the advance toward the formation of continents. This extension of the dry land was brought about not only by the gradual accumulation of materials, but also by the upheaval of large tracts of stratified deposits; for, though the loftiest mountainchains did not yet exist, ranges like those of the Alleghanies and the Jura belong to this division of the world's history. During this time, the general character of the animal and vegetable kingdoms was higher than during the previous age. Reptiles, many and various, gigantic in size, curious in form, some of them recalling the structure of fishes, others anticipating birdlike features, gave a new character to the animal world, while in the vegetable world the reign of the aquatic Cryptogams was over, and terrestrial Cryptogams, and, later, Gymnosperms and Monocotyledonous trees, clothed the earth with foliage. Such was the character of this second age from its opening to its close; and though there are indications, that, before it was wholly past, some low, inferior Mammalian types of the Marsupial kind were introduced,* and

I say nothing of the traces of Birds in the Secondary deposits, because the so-called bird-tracks seem to me of very doubtful character; and it is also my opinion that the re

also a few Dicotyledonous plants, yet they were not numerous or striking enough to change the general aspect of the organic world. This age was throughout, in its physical formation, the age of large continental islands; while in its organic character it was the age of Reptiles as the highest animal type, and of Gymnosperms and Monocotyledonous plants as the highest vegetable groups.

There was an age in the physical history of the world when great ranges of mountains bound together in everlasting chains the islands which had already grown to continental dimensions,-when wide tracts of land, hitherto insular in character, became soldered into one by the upheaval of Plutonic masses which stretched across them all and riveted them forever with bolts of granite, of porphyry, and of basalt. Thus did the Rocky Mountains and the Andes bind together North and South America; the Pyrenees united Spain to France; the Alps, the Caucasus, and the Himalayas bound Europe to Asia. The class of Mammalia were now at the head of the animal kingdom; huge quadrupeds possessed the earth, and dwelt in forests characterized by plants of a higher order than any preceding ones, the Beeches, Birches, Maples, Oaks, and Poplars of the Tertiaries. But though the continents had assumed their permanent outlines, extensive tracts of land still remained covered with ocean. Inland seas, sheets of water like the Mediterranean, so unique in our world, were then numerous. Physically speaking, this was the age of continents broken by large inland seas; while in the organic world it was the age of Mammalia among animals, and of extensive Dicotyledonous forests among plants. In a certain sense it was the age of completion, -the one which ushered in the crowning work of creation.

mains of a feathered animal recently found in the Solenhofen lithographic limestone, and believed to be a bird by some naturalists, do not belong to a genuine bird, but to one of those synthetic types before alluded to, in which reptilian structure is combined with

certain birdlike features.

There was an age in the physical history of the world (it is in its infancy still) when Man, with the animals and plants that were to accompany him, was introduced upon the globe, which had acquired all its modern characters. At last the continents were redeemed from the water, and all the earth was given to this new being for his home. Among all the types born into the animal kingdom before, there had never been one to which positive limits had not been set by a law of geographical distribution absolutely impassable to all. For Man alone those boundaries were removed. He, with the domestic animals and plants which were to be the companions of all his pilgrimages, could wander over the whole earth and choose his home. Placed at the head of creation, gifted with intellect to make both animals and plants subservient to his destinies, his introduction upon the earth marks the last great division in the history of our planet. To designate these great divisions in time, I would urge, for the reasons above stated, that the term which is indeed often, though not invariably, applied to them, be exclusively adopted, -that of the Ages of Nature.

But these Ages are themselves susceptible of subdivisions, which should also be accurately defined. What is the nature of these subdivisions? They are all connected with sudden physical changes in the earth's surface, more or less limited in their action, these changes being themselves related to important alterations in the organic world. Although I have stated that one general character prevailed during each of the Ages, yet there was nevertheless a constant progressive action running through them all, and at various intervals both the organic and the physical world received a sudden impulse in consequence of marked and violent changes in the earth-crust, bringing up new elevations, while at the same time the existing animal creation was brought to a close, and a new set of beings was introduced. These changes are not yet accurately defined in America,

because the age of her mountains is not known with sufficient accuracy; but their limits have been very extensively traced in Europe, and this coincidence of the various upheavals with the introduction of a new population differing entirely from the preceding one has been demonstrated so clearly that it may be considered as an ascertained law. What name, then, is most appropriate for the divisions thus marked by sudden and violent changes? It seems to me, from their generally accepted meaning, that the word Epoch or Era, both of which have been widely, though indiscriminately, used in geology, is especially applicable here. In their common use, they imply a condition of things determined by some decisive event. In speaking of human affairs, we say, "It was an epoch or an era in history," or in a more limited sense, "It was an epoch in the life of such or such a man." It at once conveys the idea of an important change connected with or brought about by some striking occurrence. Such were those divisions in the history of the earth when a violent convulsion in the surface of the globe and a change in its inhabitants ushered in a new aspect of things.

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I have said that we owe to Élie de Beaumont the discovery of this connection between the successive upheavals and the different sets of animals and plants which have followed each other on the globe. We have seen in the preceding article upon the formation of mountains, that the dislocations thus produced show the interruptions between successive deposits: as, for instance, where certain strata are raised upon the sides of a mountain, while other strata rest unconformably, as it is called, above them at its base,—this term, unconformable, signifying merely that the two sets of strata are placed at an entirely different angle, and must therefore belong to two distinct sets of deposits. But there are two series of geological facts connected with this result which are often confounded, though they arise from very different causes. One is that described above, in

which a certain series of beds having been raised out of their natural horizontal position, another series has been deposited upon them, thus resting unconformably above. The other is where, one set of beds having been deposited over any given region, at a later time, in consequence of a recession of the sea-shore, for instance, or of some other gradual disturbance of the surface, the next set of beds accumulated above them cover a somewhat different area, and are therefore not conformable with the first, though parallel with them. This difference, however slight, is sufficient to show that some shifting of the ground on which they were accumulated must have taken place between the two series of deposits.

This distinction must not be confound

ed with that made by Élie de Beaumont : we owe it to D'Orbigny, who first pointed out the importance of distinguishing the dislocations produced by gradual movements of the earth from those caused by mountain- upheavals. The former are much more numerous than the latter, and in every epoch geologists have distinguished a number of such changes in the surface of the earth, accompanied by the introduction of a new set of animals, though the changes in the organic world are not so striking as those which coincide with the mountain - upheavals. Still, to the eye of the geologist they are quite as distinct, though less evident to the ordinary observer. To these divisions it seems to me that the name of Period is rightly applied, because they seem to have been brought about by the steady action of time, and by gradual changes, rather than by any sudden or violent convulsion.

It was my good fortune to be in some degree connected with the investigations respecting the limitation of Periods, for which the geology of Switzerland afforded peculiar facilities. My early home was near the foot of the Jura, where I constantly faced its rounded domes and the slope by which they gently descend to the plain of Switzerland. I have heard it said that there is something

monotonous in the continuous undulations of this range, so different from the opposite one of the Alps. But I think it is only by contrast that it seems wanting in vigor and picturesqueness; and those who live in its neighborhood become very much attached to the more peaceful character of its scenery. Perhaps my readers will pardon the digression, if I interrupt our geological discussion for a moment, to offer them a word of advice, though it be uncalled for. I have often been asked by friends who were intending to go to Europe what is the most favorable time in the day and the best road to enter Switzerland in order to have at once the finest impression of the mountains. My answer is always, Enter it in the afternoon over the Jura. If you are fortunate, and have one of the bright, soft afternoons that sometimes show the Alps in their full beauty, as you descend the slope of the Jura, from which you command the whole panorama of the opposite range, you may see, as the day dies, the last shadow pass with strange rapidity from peak to peak of the Alpine summits. The passage is so rapid, so sudden, as the shadow vanishes from one height and appears on the next, that it seems like the step of some living spirit of the mountains. Then, as the sun sinks, it sheds a brilliant glow across them, and upon that follows-strangest effect of all- a sudden pallor, an ashy paleness on the mountains, that has a ghastly, chilly look. But this is not their last aspect after the sun has vanished out of sight, in place of the glory of his departure, and of the corpse-like pallor which succeeded it, there spreads over the mountains a faint blush that dies

gradually into the night. These chang

less, I would advise travellers to choose the latter half of the day and a road over the Jura for their entrance into Switzerland.*

It was from the Jura itself that one of the great epochs in the history of the globe received its name. It was in a deep gorge of the Jura, that, more than half a century ago, Leopold von Buch first perceived the mode of formation of mountains; and it was at the foot of the Jura, in the neighborhood of Neufchatel, that the investigations were made which first led to the recognition of the changes connected with the Periods. As I shall have occasion hereafter to enter into this subject more at length, I will only allude briefly here to the circumstances. so doing I am anticipating the true geological order, because I must treat of the Jurassic and Cretaceous deposits, which are still far in advance of us; but as it was by the study of these deposits that the circumscription of the Periods, as I have defined them above, was first ascertained, I must allude to them in this connection.

In

Facing the range of the Jura from the Lake of Neufchatel, there seems to be but one uninterrupted slope by which it descends to the shore of the lake. It will, however, be noticed by the most careless observer that this slope is divided by the difference in vegetation into two strongly marked bands of color: the lower and more gradual descent be

* The two most imposing views of the Alps from the Jura are those of Latourne, on the road from Pontarlier to Neufchatel, and of St. Cergues, on the road from Lons le Saulnier to Nyon; the next best is to be had above Boujean, on the road from Basle to Bienne. Very extensive views may be obtained from any of the summits in the southern range of the Jura; among which the Weissenstein above Soleure, the Chasseral above Bienne, the Chaumont above Neufchatel, the Chasseron above Grançon, the Suchet above Orbe, the Mont Tendre or the Noirmont above Morges, and the Dôle above Nyon, are the most frequented. Of all these pointe Chaumont is unquestionably to be preferred, as it commands at the same time an equally extensive view of the Bernese Alps and the Mont Blanc range.