CH. XXXIX.

SIR CHARLES LYELL.

409

some places at the rate of about two or three feet in a century; and in Greenland, where it is sinking, so that huts built near the shore have to be moved inland because they are becoming submerged in the sea.

These are a very few of the facts which you can understand, by which Lyell demonstrated that the surface of our earth is always undergoing changes in our own day, and that by similar changes going on in past times the whole of the crust of our earth may have been built up and carved out. In addition to this he showed how plants and animals are now being buried in mud and earth, and how their remains are washed into caves, or preserved in peat-mosses; thus affording us examples of the way in which the remains of ancient animals have become entombed in the earth's crust.

Thus Sir Charles Lyell taught men to read the true history of the earth. It is difficult in the present day to understand rightly how great a work he accomplished, for though his ideas were ridiculed in the beginning, yet he lived long enough to see all men agree with him, and his doctrines received as self-evident truths. Like all other great men, he was humble and reverent in his study of nature. His one great desire was to arrive at truth, and by his conscientious and dispassionate writings he did much to persuade people to study geology calmly and wisely, instead of mixing it up with angry disputes, like those which, in the time of Galileo, disfigured astronomy. He travelled a great deal, especially in America, and worked out a great many facts in geology. But in future ages his name will stand out among those of other geologists chiefly as having shown that the changes in the crust of our earth have been brought about in the course of long ages by causes like those which are still in action.

After the year 1830, when his 'Principles of Geology'

was first published, the study of this science went on very rapidly indeed. As with all the other sciences of the nineteenth century, you must read the details in special works; but there are two great discoveries which we must mention very shortly here. These are-1st. The fact that much of temperate Europe, Asia, and America was at one time covered with ice, as Greenland is now; and 2nd, that man has lived upon the earth much longer than was once supposed.

Louis Agassiz, 1807-1874.-The man whose name will always be remembered as having first traced out the wonderful history of the great ice-period is Agassiz, the famous. Swiss naturalist, who was born in 1807 at Mottier, near Neuchatel, and died in 1874 in America.

Louis Agassiz was the son of a Swiss pastor, and he forms one among many bright examples in the history of science, of men who cared neither for wealth, advancement, nor ease, but for the study of nature alone, and the grand truths to be obtained by it. After receiving a good education in the Swiss and German Universities, living frugally and economically, as students can on the Continent, he took his degree of Doctor of Medicine at Munich in 1829, having already written several important papers on zoology. In 1832 he was made Professor of Natural History at the University of Neuchatel; and in 1833 he published his work on 'Fossil Fishes,' the expenses of the book being liberally paid by Humboldt. In 1839 he published his grand work on the 'Fresh-water Fishes of Europe,' which cost him so much that he was very poor for years afterwards.

There are very touching passages in some of Agassiz's private letters at this early period, when he had a hard

CH. XXXIX.

AGASSIZ.

411

struggle with life. His enthusiasm breathes out so naturally, and he speaks so regretfully of want of money, not for himself, but the work he longed to complete; while his gratitude is so sensible and heartfelt towards those who helped him to bring out these splendid additions to the science of zoology. His was a warm-hearted, earnest, and active nature, and he was beloved by all who knew him. It is pleasant to think that the Americans, among whom he spent the latter half of his life, from 1846 to 1874, appreciated him fully; so much so that Mr. Anderson, a rich tobacco merchant of New York, presented him in 1873 with the island of Penikese, one of the Elizabeth islands, north of New York, and with funds to establish there a marine naturalist's school. The last year of Agassiz's life was spent chiefly on this island, training up a group of young naturalists.

Agassiz proves that parts of northern Europe and

North America must once have been covered with Great Fields of Ice, 1840.-It is, however, of the early part of Agassiz's life, while he was still in Switzerland, that we must now speak. Although his chief study was zoology, yet he could not live at Neuchatel, and travel about the Alps without being struck with those mighty rivers of ice, called glaciers, which creep slowly down the valley of the Alps in Switzerland, carrying with them stones and rubbish. (See Fig. 62, p. 412.)

These glaciers are formed by the snow, which collects on the tops of high mountains, and sliding down, becomes pressed more and more firmly together as it descends into the valleys, until it is moulded into solid ice, creeping slowly onwards between the mountains, and carrying with it sand, stones, and often huge pieces of rock which fall upon it. At last one end of this ice-river reaches a point where

the air is warm enough to melt it, and here it flows gradually away as water, leaving the stones and rubbish it has brought down lying in a confused heap, which is called a moraine.

Towards the end of the eighteenth century a famous geologist, named De Saussure, spent much time in examining

FIG. 62.

Glacier carrying down Stones and Rubbish (Lyell).

the glaciers of the Alps, and pointed out how they are now forming large deposits in the valleys, out of these heaps of rubbish which they bring down from the mountains. Since his time many geologists had taken up the study, but it was Professor Agassiz who first spelled out the wonderful history we can learn from it, about the former climate of our hemisphere. He noticed that rocks over which a glacier has

CH. XXXIX.

GLACIERS.

413

moved, are polished and grooved by the rough stones and sand frozen into the bottom of the ice, just in the same way as a piece of wood is scraped by the sharp iron at the bottom of a plane; and by these glacial scratches, or stria, as they are called, he could tell where glaciers had been, even though there was nothing else to show that ice had ever existed in the country.

Now, when he began to examine the slopes of the Alps many hundred feet above the present glaciers, and also in places where it is now too hot for ice to remain, he found to his surprise numbers of these glacial striæ and also remains of huge moraines, showing that the glaciers of olden time must once have been much larger and have stretched farther down the valley than they do now. And what was still more strange, these same marks were to be seen on the Jura Mountains, on the other side of Switzerland, where there are never any glaciers at present; moreover, on the Jura there were found huge blocks, some of them as big as cottages, which were not made of the same materials as the hills on which they rested, but were broken pieces of rock such as are now only found on the Alps.

It was clear, then, that these enormous pieces of stone must have been carried right across Switzerland from the Alps near Mont Blanc, and across the lake of Geneva, which is 1,000 feet deep, and then deposited on the Jura range near Neuchatel, where one block of Alpine gneiss, called the Pierre-à-Bot, as large as a good-sized cottage, sits perched on a mountain 600 feet above the top of the lake. How had these blocks travelled across the Swiss plains? No flood could have carried them, for they were too heavy, and besides they were not smooth as stones are which have been rolled in water, but were rough with sharp edges. Agassiz