the hypothesis of those who had written at first hand, and after using all the lights then existing, but who had never supposed that what they had indicated in general terms would be afterward made so definite and real to the public eye. Those untrue statements of my own I must leave, however, just as they are, and rejoice that the great advance of science has led to the accurate knowledge of the great plateaus of which the civilised world then knew but little. One word more: I fix the lower limit of plateaus of the second grade at 500 feet -lower therefore than the great master in physical geography fixed his.

"Elevations of the soil," says Humboldt, "which do not display a marked difference in climate and vegetation from the country around them, are not rightly called plateaus." His meaning is, that the name does not relate to absolute height measured from the sea, but to harmonious climatic relations existing between contiguous districts, one of which is more elevated than the other. Highland

and lowland are therefore to him words of unfixed meaning, if they do not stand in the contrast of height, climate, relief, and rates of temperature. Humboldt, therefore, did not consider the depression of central Asia at the Taringol as a plateau; and table-lands from 200 to 1200 feet in absolute elevation—i. e., from the sea-level—are passed over by him as not worthy of the same name which he applied to the plains 6000 to 10,000 feet above the sea.

Dealing as I do with the elementary features and the physical contrasts of countries which for the most part are now thoroughly explored, I prefer, for the purpose of elucidating the subject of physical geography, to consider the plateau as beginning at 500 feet above the level of

the sea. By comparing the plateaus of both hemispheres it is not difficult to deal with a variety of features, and to make a number of distinctions which, without an absolute standard, it would be impossible to make.

We pass to the consideration of the much more varied and more imposing characteristics of mountains.

MOUNTAINS AND MOUNTAIN-LANDS.

Mountain-lands cannot, strictly speaking, be compared with plateaus, except in way of contrast, because they are not uniform, broad, and sharply-defined tracts, but extend in a linear direction, having as their chief feature the longitudinal axis of the mountain-chain. Groups of mountain-ridges may be separated from each other, or may be united in any coherent way which does not make them continuous, and yet, despite the want of continuity, form a perfect whole.

Mountains, with their fissures, chasms, abysses, valleys, ravines, clefts, precipices-in a word, their varied diversities of feature broken through in every direction, the whole chain rent into fragments by these transverse breaks are in direct contrast with plateaus. They have quite often a common range of elevation, which, measured from the sea-level, is not unfrequently much greater than the districts lying at their base. Yet this relation is only incidental, it is not essential. There is no necessary connection between the height of the outlying plateau and the height of the mountain-range. In Switzerland the mountains rise to the altitude of 13,000 or 15,000 feet; the country at the foot of the Alps is but 1000 to 2000 feet above the sea. Here the distance between the sum

mit and the plateau at the base suggests no relation between them.

The distinctive characteristic of a mountain-land is the

height of isolated groups. Great differences of elevation within small distances characterise mountain-regions; small differences within great distances characterise plateaus. The plateau depends upon uniform evenness of surface, or an approximation to it, over a large extent of territory. The mountain-range is the exact opposite, the development of all kinds of extremes within a limited space, and the consequent individualisation of the locality where it stands. Mountain-lands cannot therefore be identified with the type of the highland and the plateau. The mountain-chain has a character of its own, whether existing in unbroken unity, or subdivided into subordinate ranges, ridges, and spurs, and whether the summits are conical or sharply pointed-whether also of moderate, medium, or loftiest elevation.

And high as mountains rise, their height is directly related to the depth of the depressions which form their valleys; the higher the mountain, the deeper the abyss which cleaves to the base. The immensely elevated peaks of the loftiest chains find their correspondence in the narrow ravines and the mountain lakes at the foot; the precipitous summits of the great American chain have their barrancos in the Andes and their canons in the Rocky Mountains. The valleys are in natural contrast with the summits. They have just as little of the uniformity of lowland plains as the mountain-tops have of the uniformity of elevated table-lands. They are infinite in variety, highly individualised, and always adapt themselves to the characteristics of the chain which conditions them. The mountain, too, has no uniformity in its character; it

embraces within the smallest compass the productions of all climes, and unites the characteristics of both highland and lowland. Mountain-regions have therefore had a great influence in history and in the development of humanity, even greater than the more monotonous plateaus, which in general harbour nomadic races and give little encouragement to permanently settled people. For this reason the geographer cannot, like the geologist, classify high table-lands and mountains together; he cannot draw the same inferences from the plateau as from the mountain-range: to the geographer the plateau is not a lower type of mountain, but the two, in their relations to man and to history, suggest entirely different results and condition entirely different processes.

And yet it must be confessed that mountains do stand in intimate connection with plateaus of both classes, and that the transitions from the one form to the other are well worthy of study. Yet the present lack of correct measurements has made this little understood.

It is not the element of height alone which gives mountains their significance. There are many other features which are little studied, yet of real importance. It is, however, not a matter of indifference whether a chain thrusts up its peaks 1000, 5000, 10,000, or 20,000 feet, and the height has been made, and will continue to be made, a subject of careful investigation. In reference to height, we distinguish what, in a general sense, we call mountains,* into hills, mounts, and mountains of various degrees of magnitude. Yet the height of the loftiest range, in comparison with the diameter of the earth, is

* The English does not convey adequately, certainly as idiomatic English, the variety of the German terms, Berge, Vorberge, Hochgebirge, Alps, and Riesenberge.

insignificant, only about ; and the combined mass of mountains are of no more account in comparing them with the entire mass of the globe, than the roughnesses on the rind of an apple, or perhaps more exactly still, than those on the shell of an egg. The combined mountainsystems in the world would not suffice, if transferred to the North and South Pole, to fill out the earth to such an extent that the polar and equatorial diameters would be equal.

In following out his profound scientific investigations, Alexander von Humboldt, in order to ascertain the centre of the earth's gravity, taking into account the existing elevations above the ocean level, was led to the conclusion that too great importance was formerly assigned to mountains in their relations, not to the course of history, but to the earth as subject to mathematical laws. Very careful calculations revealed the fact to him that all the mountains of France, if reduced to a level and spread out, would raise the grade of the whole country to a height of not more than 816 feet above the sea-line. All the mountains of Europe, distributed in like manner, would raise the level to only about 630 feet. In Asia the same process would make the vast plain only 1080 feet high, in North America 702 feet, in South America only 1062 feet; while the mountains of the entire globe would raise the level to only 947 feet above the level of the sea. So insignificant are the combined mountain-systems of the earth in respect to size, in comparison with the immense body on which they stand, though their importance is great when we regard their influence on the localities where they are found. Yet in this last respect mountains deserve careful study, for they not only exercise, and have exercised, a great influence over nature and man, but they