They are most

The percentage of stones present is variable. common in the hilly districts, while in the lowland region the clay may predominate. Most of them show markings all over. They vary in size from grains to blocks several feet or even yards in diameter. Their shape is peculiar. They are neither round nor oval like the pebbles in river-gravel, or the shingle of the sea-shore; nor are they sharply angular like newly-fallen débris at the base of a cliff; but seem to be like the latter in general shape with the sharp corners and edges smoothed away. They are to the geologist what hieroglyphics are to the Egyptologist-the silent but impressive records of an age long passed away.

In narrow valleys the till often accumulates in such amount as to cover the solid floor many yards in depth. In such cases, the surface may be level, and, in the subsequent periods, the streams have made excavations in the mass, leaving the till in the terrace-form. Its unstratified character will be determined by examining the earth along

the sides of the escarpment, as, superficially, it is difficult to distinguish the material from the terraces of later age.

When the till is removed from the underlying rocks, their upper surface almost invariably shows a smoothed and often highly-polished appearance, and the whole pavement is marked with those peculiar scratches or striæ that form so characteristic a feature of the embedded stones. The extent to which the polishing is carried depends very much upon the nature of the rock. As the best-preserved stones of the bowlder-clay consist of close-grained limestone and clay iron-stone, so the same materials in the ledge-condition preserve most perfectly

the fine lines of striation. The soft sandstones and highly-jointed rocks are much less finely marked, and often show a broken and shattered surface.

GREENLAND. To understand the appearance of Northern Europe in the Ice period, we may consider the features presented by a similar ice-covered country in modern times, and no country will better illustrate this phase of geological condition than Greenland. This island is almost continental in its dimensions, containing not less than 750,000 square miles, and is all a bleak wilderness of ice and snow, save a little strip extending to 74° north latitude along the western shore.

The coasts are deeply indented with numerous bays and fiords or firths, which, when traced inland, are almost invariably found to terminate against glaciers. Thick ice frequently appears, too, crowning the exposed sea-cliffs, from the edges of which it droops in thick, tongue-like, and stalactitic projections, until its own weight forces it to break away and topple down the precipices into the sea. The whole interior seems to be buried beneath a great depth of snow and ice, which loads up the valleys and wraps over the hills. The scene opening to view in the interior is desolate in the extreme-nothing but one dead, dreary expanse of white, so far as the eye can reach—no living creature frequents this wilderness-neither bird, beast, nor insect. The silence, deep as death, is broken only when the roaring storm arises to sweep before it the pitiless, blinding snow.

This represents perfectly the state of the northern part of our continent in the Ice age. We have a slight inkling of what it must have been universally, from the heroic messages sent down in the winter from the meteorological observatory stationed upon the summit of Mount Washington.

Some of the Greenland glaciers attain a vast size. Dr. Kane reports the great Humboldt glacier (see Fig. 1) as sixty miles wide at its termination. Its seaward face rises abruptly from the level of the crater to a height of 300 feet, but it is not known how deep it may extend under the sea. Another important ice-stream is the Glacier of Eisblink, on the northwest part of the island. It projects seaward so as to form a promontory thirteen miles in length. It comes from an unknown distance in the interior, and plunges deeply into the sea.

Since ice is lighter than water, whenever a glacier enters the sea the dense salt-water tends to buoy it up. The great tenacity of the frozen mass enables it to resist the pressure for a time. By-and-by, however, as the ice reaches deeper water, its cohesion is overcome, and large segments are forced from its terminal part, and floated up from the bed of the sea, to sail away as icebergs. The glacier evidently crops under the water to considerable depths, or, so long as the force of cohesion is able to resist the tendency of the salt-water to press it upward. The annexed diagram will show how the ice pushes down into the sea, carrying morainic materials at its base, which accumu

late at m; tb may show the origin of the block i, which is now going to sea as a buoy. In many cases the icebergs must carry with them stones frozen on the under side, as well as blocks perched on their backs. Dr. Kane speaks of ice-rafts, floating many miles out to seatables 200 feet long covered with large angular blocks and bowlders.

Though Greenland is said to be inhabited only upon the south and west coast, there is a record of an early settlement upon the side toward Iceland, with which there has been no communication for 400 years. The colony was planted about 1000 A. D., which flourished, and maintained intercourse with its mother-country till the beginning of the fifteenth century. Since that time, owing to the setting in of the arctic current, and the consequent gradual increase of ice upon the coast, the colony became inaccessible, and the records of it disappear from history. At various intervals between, 1579, 1751, etc., down to our own time, the intrepid Danes have striven in vain to reopen communication with their lost colony. This emerald coast, with valleys well stocked with reindeer and verdant glades, is now shut in by the pitiless ice-pack, and the fate of its inhabitants ought to excite the interest of the world. It would be very interesting to be informed of the condition of this colony: whether the increasing cold has enlarged the glaciers so as to push the dwellings out to sea, or whether the habitations are still standing, and a population has sprung up who know of the outside world only by tradition.'

Lake-Basins.-A strong argument for the former existence of glaciers over the northern regions comes from the excavation of basins from the solid rock for the reception of lakes. The country most. traversed by the ice agency abounds in these rock-hollows. It is very evident that the glacier is the only agency which can well be called upon to explain these phenomena. Running water excavates only on a descending plane. Sea-water acts upon its level, while the glacier requires only a pressure from behind to enable it to ascend mountains. The upward movement of the ice is shown by the striæ to have been exceedingly common.

The glacier grinds hardest where the steeper slope is exchanged for a less inclination of its rocky bed; the tendency of this action is to 1 Geological Magazine, vol. x., p. 541.

increase the length of the greater in elevation, or, in other words, to scoop out material from the ledges, in a part of the course, and, after the strength of the graver has exhausted itself, the ice will move up a slope with little energy. This process will excavate hollows that may ke filled with water in later times. Such are the basins of the great American lakes. The dimensions of the lakes are areally proportionate to the extent of the drainage-system in which they occur.

TILL OVERLAID WITH BOWLDER-CLAY, RIVER STINCHAR. r, Rock; t, Till; g, Boulder-clay. x, Fine Gravel, etc.

Bowlder-Clay.-There is a distinction to be drawn, in Scotland, between the "till" and "bowlder-clay." The two deposits pass into each other on the Highlands, and Mr. Geikie proposes to limit the latter to the maritime districts. The bowlders of the clay are more rough and angular than those found in the till. The annexed section. shows where the two deposits come into juxtaposition. This clay has not been met with more than 260 feet in vertical height above the sea. It contains an abundance of shells of Arctic mollusca. the "Champlain clay" of America.

Possibly it is

Antarctic Ice-Sheet.-From a study of the ice of the Antarctic Continent, it is possible to understand the origin of icebergs, and the transportation of large blocks of stone, in "erratics." The water is deep, and thus buoys, of enormous size, may float northerly for hundreds of miles.

Sir J. C. Ross attained the highest southern latitude on record, but found all his attempts to penetrate farther frustrated by a precipitous wall of ice, frequently 180 feet in height. For 450 miles he found this cliff unbroken by a single inlet. While coasting along this barrier his ships were often in danger from stupendous icebergs and thick packice, extending in masses too compact to be penetrated. At one point the ice descended sufficiently low to allow Ross to look down upon it from the mast-head. The upper surface appeared to be a smooth plain, shining like frosted silver, and stretching away as far as eye could reach into the illimitable distance. In principle, the sheet is the same with that figured in the north, but more extensive. Like this must have been some portions of the glacial sheet in Scotland, when the land was mantled in ice-covering, filling up the intervening straits and channels of the sea, and terminating far out in the Atlantic Ocean, in aflat-topped vertical cliff of blue ice.