and Hecla may be taken as familiar instances of volcanic accumulations, and as these have added hundreds of feet to their height, and cast their discharges for miles around during the current epoch, so have all other active volcanoes been similarly adding to their altitudes and lateral dimensions. One has only to cast his eye over a map of Volcanic Lines and Centres to see what a large area of the globe must have received accumulations of this kind within modern times-partly as mountain masses piled up on land, partly as islands upheaved from the sea, and partly as submarine sheets that have flowed as lava, or been cast abroad in showers of dust and ashes. All along the Andes, Central America, Mexico, the West Indies, and the north-western shores of the New World, volcanic accumulations have taken place, and are still taking place, on a grand scale. The same may be said of the Aleutian Islands, Kamtchatka, Japan, the Philippines, and the East Indian Archipelago; while over the bosom of the Pacific, along the Atlantic islands of Africa, in the Indian Ocean, in the Southern Ocean (as New Zealand), and in the Northern (as Iceland), similar phenomena have marked the course of the Tertiary period, and must, if we can judge from their present displays, have materially contributed to the exterior crust of our planet. Indeed, as there is no other Recent formation more obvious in its character and mode of accumulation, so there is none more rapid and gigantic in its resultsa few months being often sufficient to pile up hills of slag and scoriæ, or spread abroad sheets of lava hundreds of feet in thickness, and many square miles in extent.* But it is

* Sir W. Hamilton reckoned the current which reached Catania in 1669 to be 14 miles long, and in some parts 6 wide; Recupero measured the length of another, upon the northern side of Etna, and found it 40 miles; Spallanzani mentions currents 15, 20, and 30 miles; the stream that flowed from the Skaptar Jokul in Iceland in 1783 was about 50 miles

not to the mere volcano alone that we must look for the full effects of vulcanic energy. The earthquake and crustmotions alluded to in a former Sketch (No. 3) are in like manner ever busy in moulding and modifying the earth's exterior the former fracturing and fissuring the rocky crust, and giving tenfold significance to the discharges of the volcano, the latter silently elevating the sea-bed into dry land, or submerging the dry land beneath the waters.

Such is a rapid sketch of the Post-Tertiary or Quaternary formations, which, though recent and superficial to us, will become old and deep-seated to the observers of future ages. Scattered over the land, and spread out under the waters, they are not only everywhere present, but of all dates, from the accumulations of the current century back to those that mark the close of the glacial epoch. Indeed, the main difficulty connected with them is to assign their respective dates, and fix a scale of chronology that will be at all generally applicable. Superposition can only be applied in very limited cases; and mineral composition is of little avail, as the older are often as loose and unconsolidated as the younger. The only satisfactory test is fossils, striking back from the existing flora and fauna of any locality to those that have been removed from that locality, and from these back to such as have become totally extinct. In this way we may speak of Upper, or those containing existing plants and animals; of Middle, or those characterised by plants and animals locally extirpated; and Lower, or those marked by organisms now wholly extinct. As regards Man, they

long, by 12 or 15 in its greatest breadth, and from 20 to 600 feet in thickness, according to the nature of the ground; while Dr Coan estimates the discharge of Mauna Loa (one of the Sandwich Island volcanoes) in August 1855, at 70 miles long, with a varying width from 1 to 5 miles, and from ten to several hundred feet in thickness.

may be arranged into Pre-human and Human—the former containing no traces of man or of his works, the latter being here and there characterised by such remains. And even this Human period may be conveniently subdivided into Prehistoric and Historic,-the former, like the flint implements, shell-mounds, and cave-dwellings, dating back far beyond the reach of history-the latter coming within periods to which we can assign something like a date in years and centuries. But whatever the arrangement, we clearly perceive that some are very ancient-so ancient as to merge into the close of the glacial period, and others very recent -so recent as to be still in progress of formation. Nor let it be imagined that, because recent, these accumulations are limited and insignificant. All that is necessary to make them rival the older formations in extent and thickness is time, and this is an element as unlimited in the future as it has been prodigal in the past.

During the deposition of the more ancient, the mammoth, woolly-haired rhinoceros, hippopotamus, cave-lion, cave-bear, hyæna, and great Irish deer, were inhabitants of Western Europe; herds of mastodon roamed over the river and lake flats of North America; the plains of South America were densely peopled by the megatherium, megalonyx, glyptodon, mylodon, and macrauchene; and Australia, with more gigantic forms of kangaroo and other marsupials. At this period we have no traces of man save in Southern and Western Europe (the only tracts yet sufficiently examined); and there savage races seem to have lived in caves and wigwams, fashioned stone and flint implements,

*

* We do not lose sight of the fact, that implements fashioned out of the native quartzite of India have been found in the alluvial laterite of Madras and North Arcot, but merely hold it subordinate till the discovery of associated organisms enables geologists to form a more definite idea of the relative antiquity of these lateritic deposits.

S

and subsisted chiefly by hunting and fishing. During the deposition of the less ancient or middle formations the earlier fauna had in a great measure disappeared, and species of ox, deer, horse, wild-hog, wolf, bear, and other existing genera had taken their places. To this period belong the extinct species of ox, horse, and deer, which have been found alike in Europe and America; and perhaps also the gigantic ostrich-like birds of Madagascar and New Zealand-the æpiornis, dinornis, palapteryx, and their congeners. The men of Western Europe still fashion their stone and bone tools and tree-canoes; but traces of underground stonedwellings, and pile-dwellings in lakes, with doubtful indications of metal implements, bespeak an advance and mark the first stages from savagery to civilisation. During the deposition of the more recent, the flora and fauna of every region have remained much as we now behold them.* A few general extinctions, like the dodo, solitaire, great auk, and rhytina,+ have been recorded; hundreds of local extirpations and removals (like the original flora and fauna of our

*

According to Professor Heer, the native flora and fauna of Switzerland have remained much the same since the time of the earliest lake-dwellings, while the cultivated plants and domesticated animals have passed into totally different varieties. If this observation be correct, it tends to show that organic changes are slow or rapid in proportion to the physical changes to which life is subjected, and that where the physical surroundings undergo slow and gradual mutations (which is the common course of nature) plants and animals may exhibit little variation for ages. It is thus that the specific changes recorded by Paleontology afford the strongest evidence of the incalculable lapse and length of geological time.

The circumstances connected with the extinction of the dodo, solitaire, and great auk, are well known. The rhytina, a phytophagous Sirenian, discovered by Steller on Behring Island in 1741, is also considered as completely extirpated-the last individual having been killed in 1768. Unlike the manatees or sea-cows, the rhytina was edentate, having special bony palatal apparatus for the crushing of its food. Its subfossil remains (from 8 to 24 feet in length) are now eagerly sought after for our public museums, and one or two specimens, we believe, were exhumed in 1864.

own islands) have taken place under the aggressions of man; and man himself has risen through the successive stages of stone, bronze, and iron, to what we now behold him. We pass from pre-historic to historic times, but still there is no cessation. The agencies of nature are as busy now in moulding and remodelling the rocky crust as ever they were. From their slow and gradual operation we may fail to appreciate the results; to the future, however, they will appear in all their vastness and universality.