great convulsions which reach back into the remotest geological periods, the surface of the continents must have been subjected to frequent partial changes of level. The surface undulated probably in that same wave movement which is now observable, though in much less degree, in those earthquakes and upheavals which the whole western part of South America is experiencing

even now.

The depressions which have assumed a permanent form since the convulsions which formed them, have gradually filled with deposited soil, and, were the naturalist able to lay bare the primitive rock, he would discover that it exists in the shape of great concavities, without a trace of that evenness which now characterises the surface. Eichwald has made it probable, by his personal observations, that the upheaval of Ararat and of the Armenian plateau on which this trachyte mountain rests, has driven the Caspian Sea back east of the flat steppe of Karabagh and Mogan, on the lower Aras, to the neighbourhood of Baku. The water of that sea formerly extended to the confluence of the Bargaschad (called also Berguschat and Bergumet) with the Aras, below Ireben. The traces of volcanic action there are unequivocal: the Caspian reached, before that action occurred, up what is now the valley of the Aras, as far as Ararat; and in many places south of Erivan— at Saliyan, in Shirwan, and elsewhere-salt beds of the most crystalline quality forming whole mountains, and belts of salt lakes at the confluence of the Aras and the Kur, demonstrate their formation in a former sea which once covered that region. The very recent upheaval of the Ural chain cannot fail also to have had an influence in contracting the dimensions of the Caspian hollow.

Only two kindred depressions to this remain to be

spoken of, one of which, though not of such extent, is of still greater depth-the depression of the Jordan valley, and the bitter salt lakes on the isthmus of Suez. These we must consider before we pass from the contrasts between highlands and lowlands to the transitions between them.

THE DEPRESSION OF THE JORDAN VALLEY AND OF THE DEAD SEA.

The nearest resemblance to the Caspian hollow is found near the heart of the Old World, in the comparatively diminutive and isolated valley of the Jordan, including the Dead Sea, whose absolute depth below the level of the ocean has been determined only very recently. Many former travellers had noticed, in the deep gulf which holds the Dead Sea, and especially at its north end, near Jericho, a much greater degree of heat than elsewhere in Palestine, and the existence of many plants and fruits which they had met in the hotter climates of Arabia and India. The tree which yields the Mecca balsam flourishes in the oasis of Jericho; the product of the balsam of Palestine supplied the pin-money of Cleopatra. A number of German and English observers endeavoured to solve the question of the depth of the Jordan basin-Von Schubert, Russegger, Von Wildenbruch, Moore and Bake, and subsequently Symonds and Lynch; De Berton and Russegger made the first barometrical observations at the Dead Sea, but they did not attempt to give more definite limits to their results than to assert that its surface is somewhere between 500 and 1100 feet beneath the ocean level.

Von Schubert's barometer did not suffice to determine

this point, but he ascertained the surface of Lake Tiberias to be 535 feet below that of the Mediterranean. All barometrical measurements were unreliable at that depth; yet it was certain that the depression could not be an insignificant one. A measurement with the level made by Symonds, an Englishman, from Jaffa to the Dead Sea, in 1843, gave us our first sure results. The surface of the lake, according to him, lies 1231 feet beneath the level of the Mediterranean at Jaffa. The subsequent expedition of the Americans-Lynch, Dale, and Anderson, in 1848-has given the following additional results :—

The surface of Lake Tiberias lies beneath the ocean-level, 612 ft. the Dead Sea 1235

Soundings of the Dead Sea, made with the greatest care, determined the depth to be, according to Lynch, 1227 feet; according to Symonds, 1970 feet. The entire depression below the ocean level would be, then, by Lynch's measurement, 1235+ 12272462 feet; according to Symonds's, 1235+ 1970 = 3205 feet.

This is the Jerusalem lies

greatest known depression on the globe. 2449 feet above the ocean-level. From the roofs of the city to the surface of the Dead Sea is, therefore, 2449 + 1235 = 3684 feet; and the entire descent from the capital to the bottom of the Dead Sea is 4911 feet, if we adopt Lynch's measurement, and 5654, if we follow Symonds's.

The basin of the Dead Sea consists of two very different parts-the larger and deeper northern one, the smaller and shallow southern one; the two being separated by a sandy peninsula-el Mesraa-and connected by a narrow channel of insignificant depth. The northern basin seems to owe its present form to the unchanged

primitive depression; the southern one to a partial upheaval at some later epoch. But in breadth they do not vary much one from the other; both have their larger axes coincident with the Jordan valley, which here widens a little, but which is still hemmed in, as it is farther north, by the parallel ranges of mountains. The chain east of the sea appears to rise a thousand feet higher than the one west of it. The depths of the two basins are entirely unlike. The southern is nowhere more than 12 feet deep, and diminishes to 5 feet and less than this near the shores, so that this portion is entirely unnavigable by craft of any size; and those who wish to land have to wade for a long distance through mud as deep as their ankles. The northern part, on the contrary, attains a uniform depth of more than 1000 feet, from the north to the south; in the northern third it is even 1227 feet; toward the west coast it shoals to between 600 and 800 feet, but is 500 feet deep hard by the coast. There is but a very narrow rim of shallow water on the western side, and the navigation is, therefore, tolerably safe. On the eastern shore the coast is even bolder, and the descent to deep water immediate. Close by the romantic mouth of the Arnon, embouching through rocks, the depth of the sea is about 1052 feet. So great a difference in the depth of the two basins seems to indicate a considerable diversity in the manner of their formation.

Volcanic activities have been felt in the Jordan valley up to the present time. They manifest themselves in various forms-deposits of salt, hot and naphtha springs, asphaltum beds, sulphur fumes, currents of heated air, clouds of smoke, and rumblings beneath the surface. The valley remained, from Lake Tiberias downwards, unfilled, as we should infer from analogy that it would be

The

by the upheaval of a chain of volcanic mountains; or by the expansion of an internal lake or sea, the waters accumulating till at last they should acquire such volume as to break away and form new channels. In case the obstructions were too great, they would remain inland lakes. And such is the Dead Sea, its southern border being too high to allow it a free exit into the Red Sea. Many other fissures or hollows on the surface of the continents would be regarded as lowlands, were they not filled with water. The bottoms of such lakes often sink suddenly to a great depth, while others are lagoon-like, or shallow seas of an entirely different hydrographical character. Internal lakes, regarded as isolated lowlands, merely filled with water, are an especially interesting theme of study; yet much remains to be investigated regarding their structure and historical formation. Dead Sea has been regarded, up to this time, as the deepest of all such lakes. The greatest depth of the Caspian has not yet been fully ascertained; but if Hanway's soundings, 2700 feet, are to be relied on, it is very great. Lake Baikal, in its deepest part, between the two steep walls of rock which rise high above the surface, has not yet been carefully sounded; but as its surface is 1500 feet above the sea, its bottom does not probably fall below the ocean level. The great chain of North American lakes, whose area embraces about 109,500 square miles, are surrounded by level country from 500 to 600 feet above the sea-a region which, in part, falls under the designation of plateaus of the lowest class, and which, in part, comes under the name of lowland; the surface of Lake Superior being 628 feet above the sea, Lakes Michigan and Huron 578 feet each, Lake Erie 565 feet, and Lake Ontario 262 feet. The three first named,