6. Generally speaking, the reliefs go on increasing from the poles to the tropical regions. The highest elevations, however, are not placed at the equator, but in the neighborhood of the Tropic of Cancer, in the Old World, (Himalaya, 27° north lat.,) and near the Tropic of Capricorn, in the New World, (Nevado de Sorata, 18° south lat.)

I notice here one of the great compensations, one of the great harmonies, of nature. The effect of this law of arrangement is, to temper the burning heats of these regions, and to give them such a variety of climate as seems not to belong to these countries of the globe. If this order were reversed, and the elevation of the lands went on increasing towards the north, the most civilized half of the globe, at the present day, would be a frozen and uninhabited desert.

7. In fine, a common law combines in a single great fact all we have just said upon the general reliefs of the continent; it may be thus expressed :

All the long and gentle slopes descend towards the Atlantic and towards the Frozen Ocean, which is only a dependence of it; all the short and rapid slopes, or counter-slopes, are directed towards the Pacific Ocean and towards the Indian Ocean, which is its continuation.

In this point of view, these two great oceans appear as two basins of different geological character.

The Pacific Ocean seems an immense basin which has sunk down, and whose high and ragged edges present on all sides the abrupt terminations of the continents. It is on this great line of fractures, on the borders and all round this ocean, as has been pointed out by Mr. von Buch and other scientific men, that we behold the

great majority of the active volcanoes of our globe, arranged like an immense burning crown. If we add to this feature the multitude of volcanic islands scattered over the ocean, we comprehend the idea, expressed by Steffens, that the vast basin occupies the place of a continent of the early ages, uniting the two worlds, but sunk and submerged at present under the deep waters of the ocean, in consequence of one of the latest great revolutions of our globe.

The Atlantic Ocean, on the contrary, would be a simple depression, somewhat in the form of a trough, owing, perhaps, to a lateral pressure, and partly to the tilting motion which lifted up the lands in the neighborhood of the Pacific. Hence, its narrower breadth, the valley form, the absence of numerous islands in the interior of its basin, and the descent of all the neighboring continents by gentle slopes. Nevertheless, if we suppose the lateral force that pressed it in to have been very strong, we may conceive that this valley has a great depth.

Thus, then, gentlemen, a great law, a general law, unites all the various systems of mountains and of plateaus that cover the surface of our globe, and arranges them in a vast and regular system of slopes and counter-slopes. Considered with reference to the present state of geology, this result is astonishing. The study of the relative ages of the different systems of elevations, teaches us that each of them has existed a long time separately. One appeared in one country at a given epoch, another in another. The continents are only formed, so to speak, by piecemeal, in the train of the geological epochs; and, nevertheless, the definitive

result makes a whole, composed of parts subordinated to each other in a certain system, which might be called an organism in this order of things.

This is not the moment to press the consequences of so remarkable a fact. It is enough for me to have pointed it out to your attention.

I will add only, that the geological researches place beyond a doubt the existence of an intimate relation between the height of the mountains and of the plateaus, and the epoch of their appearance above the surface of the oceans. The most ancient chains of mountains are the least elevated; while the colossal grandeurs of the Andes and the Himalaya bear the traces of an upheaval comparatively very recent. In America, from the coasts of Brazil to the high table lands of Bolivia, and from the Atlantic shores to the Rocky Mountains; in Europe, from the mountains of Scandinavia to the summit of the Alps, we meet with upheavings successively less ancient. In the two worlds the continental masses have then become greater in the lapse of the ages, not by chance, but in two determinate directions; that is, in a geographical order, from the north to the south of the Old World, and from the east to the west in the New; and I think we may hence infer, that from the moment when the oldest lands we know emerged, the continents have had a tendency to form themselves on the spot where they now are.

We see that here, as elsewhere, all is done with order and measure, and according to a plan which we shall have a right to believe was foreseen and intended, when we shall have studied all the consequences of this arrangement of the continental masses.

LECTURE III.

Distribution of the table lands, the mountains, and the plains in the different continents; the Old World that of plateaus, the New World that of plains The basin of the oceans; this inquiry completes the study of the plastic forms of the earth's crust — Division and characteristics of the oceans; their contours and their depth Comparison of the latter with the mean elevation of the continents Conclusions ·Necessity of considering the physiology of the continental forms-Point of view which should be taken. -Law of the development of life.

LADIES AND GENTLEMEN :

In our last lecture we carried our examination into the general forms of relief of the continents. Our investigation has permitted us to establish the existence of a great common law of slopes and counter-slopes, of increase and decrease of reliefs. The entire continents, as well as the mountains, have two principal unequal slopes; the long and gentle slopes descend towards the Atlantic and Frozen Ocean, the short and steep slopes towards the Pacific Ocean.

To finish this subject, it remains to say a word upon the distribution of the table lands, of the mountains, and of the plains in the different continents.

The distribution of these three great forms of relief — is it uniform or not? Or are there not some characteristic differences, to be pointed out in this regard, between the continents? Does not the form of the elevated table lands prevail in one part of the world, the form of the

plains in another, the form of the mountains, finally, in yet a third? If we call to mind the important influence each of these forms exerts on the climate, the productions, and on the conditions of existence, and growth of the nations, we shall regard this question as one of those which most concern our subject.

Considered in this point of view, the continents present, in reality, remarkable differences.

The Old World, as we have learned from the study of its reliefs, is that of table lands and mountains. No continent exhibits plateaus so elevated, so numerous, so extensive, as Asia and Africa. Instead of one or two chains of mountains, like the Andes, Central Asia is traversed by four immense chains, supporting vast table lands of from 5,000 to 14,000 feet in elevation, and the loftiest mountains of the globe.

The extent of this elevated region is more than 2,400 miles long, by 1,500 miles broad. The principal mass of Western Asia is nothing but a plateau, from three to six thousand feet in height. Africa, south of Sahara, seems to be only an enormous pile of uplifted lands. It has been calculated that the mountains and plateaus of Asia cover five sevenths of its surface, while the plains occupy only two sevenths. In Africa, the high regions form two thirds of the continent, the plains only one third.

If I call the Old World the world of plateaus, it is not because great plains are wanting there. The whole north of Europe and of Asia is merely a boundless plain, and from the shores of Holland, through Germany, Russia, the Steppes of the Caspian and Siberia, the raveller may cross the Ancient World from the Atlan