we actually have,-nor more than 400,000,000 years ago, or we should not have so much as the least observed underground increment of temperature. That is to say, I conclude that Leibnitz's epoch of 'emergence' of the consistentur status' was probably within these dates,"* III. THE GLACIAL PERIOD IN THE SOUTHERN HEMISPHERE. By THOMAS BELT, F.G.S. HE tablets on which the ice of the Glacial period left its record in the southern hemisphere are probably now mostly covered by the sea, and we cannot trace its progress and extent with the same facility and certainty as in the northern temperate regions. Yet notwithstanding this, and also that the land surfaces of the South that have been glaciated have not been studied to anything like the same extent as in Europe and North America, points of resemblance are apparent, and grounds exist for the belief that both hemispheres have passed through a somewhat similar glacial experience. In our hemisphere, I have sought to show in former papers, there were two ways in which the ice spread. One was an accumulation on mountain-chains, and a radiation from them over the surrounding country. The other, and I think by far the most important, was the gradual advance of a ridge of ice down the bed of the North Atlantic, and probably also of the North Pacific, which blocked up the drainage of the continents as far as it extended, and caused enormous lakes of fresh or brackish water and immense destruction of life amongst the animals that were caught on the plains by the rising floods. The marks left by the Atlantic ice are seen in Europe, as far as the southern extremity of Ireland, and in America, to the south of New York, and beyond these points, its further progress can be traced by the evidence of the interruption of the drainage of the continents as far as the northern slopes of the Pyrenees on one side of the Atlantic, and to the coasts of Trans. Roy. Soc. of Edinburgh, vol. xxiii., p. 161. Virginia on the other. The real markings on the rocks, however, have not been traced in Europe farther south than 51° N. lat., and in America than 40° N. lat., excepting those of the ice that proceeded from the mountain ranges. In the other hemisphere, within the distance from the Southern Pole that the ice has been shown by actual markings on the rocks to have reached from the North Pole on the European coasts, that is, to latitude 51° N.,-there are no large masses of land, excepting the extreme end of South America and the Antarctic continent. And if we take a corresponding circle in the south to the limit the ice has left its marks in America or to lat. 40°, we shall still only embrace Patagonia in South America and the Middle Island in New Zealand. Even if we take the furthest limit of the extension of the Atlantic ice, as shown by its interference. with the drainage of the American continent, we only bring South America as far north as the Rio Plata, and New Zealand and Tasmania, with the southern end of Australia, within the area where we could expect to find any similar evidence on the supposition that in the Glacial period the ice extended everywhere as far from the Southern Pole as its extreme limit reached from the Northern. The conditions are therefore very different in the two hemispheres. In the one, broad continents stretch from within the Arctic circle toward and up to the Equator; in the other, nearly the whole of the temperate zone is covered with water. If, then, there were much less evidence than there is of the glaciation of southern lands, we need not have been surprised; but of late there seems to have arisen an idea amongst some geologists that there is no evidence. in the southern hemisphere of the occurrence of a Glacial period, and it may be useful if I bring together what has been described, and show how far the phenomena agree with those of the northern hemisphere. Commencing in America, immediately south of the Equator, we have first to deal with the remarkable theory of Agassiz, that the great valley of the Amazon was once filled with ice flowing from the distant Andes, which left an enormous terminal moraine on the Atlantic coast. This moraine he supposed blocked up for a time the waters of the great valley, and caused the deposition of various stratified deposits covered by a peculiar drift clay that rarely contains transported boulders. I have examined this deposit from Pernambuco northwards through the provinces of Ceara and Maranham, as far as Para. In some parts it is composed of small angular fragments of rock, cemented together by an ochraceous clay, and resembling the breccia at the base of the Permian rocks in Westmoreland. In others it is a ferruginous clay, containing few stones, but with a layer of quartz pebbles at its base. It is not confined to the valleys, but wraps over the hills like a mantle. Now and then it contains large boulders of granite, but I could never satisfy myself that these might not have been left during the decomposition and denudation of the rocks of the neighbourhood. It differs much from any glacial deposit I have seen, and I am sorry that I can neither suggest any theory to account for its origin nor agree with that of the illustrious Agassiz. To the latter there seems to me insuperable objections. There are no moraines in the valley of the Lower Amazon. The terminal one might have been, as Agassiz suggests, washed away by the waves of the Atlantic, but the great glacier ought to have left others to mark the various stages of its recession. No remnant of these has been found, and we cannot believe that a glacier that left a huge moraine stretching for hundreds of miles across the whole seaward front of the Amazon Valley should have shrunk back for more than 1000 miles without leaving any whatever to mark its retreating course. The Valley of the Amazon abounds with birds and beasts, many of which are found nowhere else. Peculiar species of fishes swarm in the river and its tributaries. If the great valley was filled with ice, where did these find a refuge? To Agassiz this did not present any difficulty, as he believed that the present inhabitants of the world had been created since the Glacial period; but to those who hold the opinion that they are descended from pre-glacial ancestors, and that since the Glacial period there has not been much variation, the peculiar genera and species of the fauna of the Amazon Valley present serious objections to the theory. Had Agassiz found in the Valley of the Amazon what he considered moraines, I should have had much difficulty in believing that he was mistaken, for no man had more experience of ice-action, present and past. Before him, Charpentier and others had worked out the conclusion that the glaciers of the Alps had in former days stretched far beyond their present limits, but they referred that extension to an elevation of the mountains, and not to a change of climate that affected all the northern parts of the continent. Agassiz accepted the theory, at first, that the upheaval of the Alps must, in some way or other, have been connected with the phenomena, but further study led him to abandon it, and conclude that the climatic conditions could not have been local, but must have been cosmic. "When," he says, "Switzerland was bridged across from range to range, by a mass of ice stretching southward into Lombardy and Tuscany, northward into France and Burgundy, the rest of Europe could not have remained unaffected by the causes which induced this state of things."* Agassiz was thus the founder of the theory of a "Glacial Period," and in Great Britain, in Scandinavia, and in North America, evidence was soon found, and has been ever since accumulating, attesting the truth of his grand generalisation. He was not likely to be mistaken as to what constituted a moraine, but he found none in the great valley, and he says himself that he had not here the positive evidence that had guided him in his previous glacial investigations.† Not so, however, with regard to his discovery of the marks of glaciation on the mountains of Ceara. Here, only about three degrees south of the Equator, he found undoubted moraines blocking up the valleys, and the evidence of glacial action was to him as clear as in the valleys of Switzerland, of Scotland, and of the Northern States of America.t This is the nearest point to the Equator at which glacial moraines have been found. On the other side of the line I found huge moraines in the northern part of Nicaragua, near the boundary between it and Honduras, in lat. 13° 47' N. This is the farthest south that glacial action has been traced in the northern hemisphere. Prof. W. M. Gabb has informed me that in his geological researches in the mountains of Costa Rica he found no evidence of glaciation. Between the moraines of northern Nicaragua and those of the mountains of Ceara there is an area comprising about 17° of latitude, and including most of Nicaragua, the whole of Costa Rica, of Columbia, of Equador, and of the great valley of the Amazons, in which no certain signs of glaciation have been seen. This wide region includes several large zoological sub-provinces, characterised by highly peculiar tropical genera, and a wealth of species not met with elsewhere on the continents to the north and south. Within this area are large groups of insects the extreme forms of which are linked together by a series of gradations, and every district has its representative forms of types that run through the whole. But as we travel south from the unglaciated districts lying between lat. 14° N. and lat. 3° S. the species become more and more separated; the genera comprise species as far removed from each other as before, but these are not connected by the same intermediate forms. These gaps become wider and wider as we get farther south, until at the extreme end of the continent, where the rocks are glaciated from ocean to ocean, isolation, and not affinity, is the characteristic of the fauna, which is made up of waifs and strays that appear rather to have struggled in from the outside, upon a country that had been depopulated, than to have been developed within it. In the glaciers of Ceara and northern Nicaragua we find the first parallel between the glaciation of the two hemispheres; and it is to be noted here, as it may be elsewhere, that there appears to have been more ice heaped up on the southern half of the world than on the northern, the much nearer approach of the glaciers to the Equator in Brazil than in Central America being the first evidence of it. This was probably due, not to greater cold, but to greater precipitation, proportional to the vast evaporating area of the Southern Ocean. * Travelling southward, we find that Mr. David Forbes noticed in Bolivia great accumulations of detritus with grooved stones and deeply-furrowed rocks, resembling those that he was familiar with in Norway. And on the opposite side of the continent, near Rio Janeiro, Prof. Hartt has described moraines left by glaciers that formerly came down from the mountains of Tijuca.t Still farther south the evidences of glacial action increase. For the description of the phenomena of La Plata, Patagonia, and Chile we must still turn to the observations of Darwin made more than forty years ago, which, when we consider that the glacial theory was in its infancy, evince the same rare powers of acute observation and philosophical generalisation that have since made his name so famous. Ascending the River Santa Cruz, Darwin found, at a distance of about 100 miles from the Atlantic and at a height of about 1400 feet above the level of the sea, a great abundance of large angular boulders that had been transported from the Cordillera, the nearest slope of which was still about 60 miles distant. On both sides of the continent from lat. 41° S. to the southern extremity of it, he considers there is the clearest evidence of former glacial action in numerous immense boulders transported far from their parent source.‡ *DARWIN, Origin of Species, Sixth Edition, p. 335. |