Agricultural Counties. Counties. Nithsdale and Annandale DUMFRIES. Wigton, or East Stranraer, PERTH. rie, Strathearn, Monteith, Breadalbane Athol, and Fife Dunferm line, CUPAR. CLACK MANNAN. Clackmannan Kinross Forfar, or Angus Kincardine, or STONESHAVEN. NAIRN. Strathspey Nairn Bute, Arran, the Cumbraes, and Ailsa Craig, in the Frith of Clyde. The Inner Hebrides, includ ing Gigha, Islay, Jura, The Outer Hebrides, includand Harris, ing Lewis North Uist, South Uist, Benbecula, the Barra Group, &c., lying to the Northwest of the Inner Hebrides. St. Kilda, West of the Outer Hebrides. The Orkney Islands, including Pomona, Hay, North Ronaldshay, South Ronaldshay, Westray, Rowsay, Stronsa, &c., lying to the North of Caithness. The Shetland Islands, includ. ing Mainland, Yell, Unst, Fetlar, Whalsay, Bressay, Foula, &c., lying to the North of the Orkney Is lands. The Bell Rock, near the mouth of the Tay. May, Inchkeith, the Bass Rock, &c., in the Frith of PENINSULAS. Cantire, in Argyleshire. Storr Head, and Cape Wrath, in Sutherlandshire. Dunnett Head, and Duncan's bay Head, in Caithness. Tarbet-ness, in Ross-shire. Kinnaird's Head and Buchan ness, in Aberdeenshire. Fife-ness, in Fifeshire. St. Abb's Head, in Berwick shire. CHAPTER III.-ON THE INFLUENCE OF ATMOSPHERIC AGENTS ON THE EARTH'S CRUST. i. ON THE FORMATION AND ASPECT OF GLACIERS. AMONG the geological agents that have produced great and extensive changes in the crust of the earth, there are none that have played a more important and mysterious part than what are called glaciers [pronounced glass-yeh]. Geologists have ascribed such remarkable and so many physical phenomena to the agency of glaciers, that it is indispensably necessary for the student to have a distinct idea of the formation, the extent, which is rendered "Sea of Ice." This French name, and the English translation of it have given to the majority of readers, some erroneous ideas of a glacier. Some have regarded a glacier Alpine ridges, or a collection of land-locked water, frozen up as being a frozen lake, embedded in some deep hollow among into a mass that never melts. Others have thought that a glacier is an immense collection of mingled snow and ice, that have settled down as a confused heap, in some deep glen or Fig. 82. tion of a glacier is to imagine that a balloon has set you down quietly on the summit of Mont Blanc, and that from that point down towards some of the valleys, you are observing the glacial phenomena around you. To aid your imagination and study, examine closely the details of the engraving of Mont Blanc, given in our last lesson, page 248. As you are walking down from the higher ridges, you find that the snow at that high elevation, is very different from the snow that you have been accustomed to in the lowlands. In England the snow lies in flakes, and soon becomes clammy and adhesive; but in the loftier regions of the Alps, all the snow about you is granular, and partly globular like small shot. All the snow there is in grains, and not in flakes. In your walk over this snow, you sink at every step, as if you had to walk over the floor of a room where the gardener or farmer keeps teaux, on which the snow rests, would become higher and higher, at the rate of about an inch every year. This gradual rising in elevation would, if nothing counteracted it, attain to a great height in a thousand years. This counteraction takes place by the subsidence or the sinking of the firny snow that lies in masses on the solid rocks, down towards hollows and and defiles among the mountains, where it eventually becomes concreted into glaciers. In descending the higher slopes, you find that the firny snow begins to cease to be granular and loose. It looks and feels under your feet as if it had been penetrated by thaw moisture and then re-frozen. Its texture is now more compressed; its particles adhere closer and firmer to each other; and it is more of a compact mass. This change of texture is effected in summer. It melted in the day; it froze again at night. This mass, his store of peas or rice, into which you sink ankle deep or knee deep, according to the thickness of the bed of peas or rice over which you have to pass. It is so This kind of snow does not stick like flaky snow. loose, like the peas or shot, that you cannot make a snow-ball of it. Though this kind of snow is sometimes seen in England on a day of very severe frost, yet we have no word to distinguish it from the snow which fails in flakes. The inhabitants of the Alps, however, have distinct names to designate this particular kind of granular snow. The Germans call it FIRN, and the French, NEVE. In our present lesson, I shall call this kind by the name of firny snow. Among the higher ranges of the Alps, that is, at any elevation above 8,000 feet, the last year's snow never melts away tompletely in the summer: consequently the mountain pla then, after successive thawings and freezings, undergoes a fresh crystallization and is formed into coarse ice, forming a hed that extends downwards to a deep valley below you. The line which marks this change in the firny snow, points out the origin of the glacier. This altered or transformed Firn is the source of the glacier. The glacier is only the drain of this Firn. The naturalist Hugi has shown that this line, or point of temperature at which firny snow changes into glacier ice is, in the Alps, invariable; it is at the height of 7,800 feet above the level of the sea. You will do well to keep in mind that a glacier consists of firny snow, partly melted and then recongealed, and in that state pressed into valleys or glens, where it is converted into perpetual ice. The ice, however, of the glacier is not like that which you see formed by the freezing of water. In the glacier, the ice is less dense and com |