228 AGE OF MAN PREGLACIAL. CHAP. XII. to the boulder clay, No. 4, pp. 213 and 224. The position of the Hoxne flint implements corresponds with that of the Mundesley beds, from A to D, p. 224, and the most likely stratum in which to find hereafter flint tools is no doubt the gravel A of that section which has all the appearance of an old river-bed. No flint tools have yet been observed there, but had the old alluvium of Amiens or Abbeville occurred in the Norfolk cliffs instead of the Valley of the Somme, and had we depended on the waves of the sea instead of the labour of many hundred workmen continued for twenty years, for exposing the flint implements to view, we might have remained ignorant to this day of the fossil relics brought to light by M. Boucher de Perthes, and those who have followed up his researches. Neither need we despair of one day meeting with the signs of Man's existence in the forest bed No. 3, or in the overlying strata 3', on the ground of any uncongeniality in the climate or incongruity in the state of the animate creation with the well-being of our species. For the present we must be content to wait and consider that we have made no investigations which entitle us to wonder that the bones or stone weapons of the era of the Elephas meridionalis have failed to come to light. If any such lie hid in those strata, and should hereafter be revealed to us, they would carry back the antiquity of Man to a distance of time probably more than twice as great as that which separates our era from that of the most ancient of the tool-bearing gravels yet discovered in Picardy, or elsewhere. But even then the reader will perceive that the age of Man, though preglacial, would be so modern in the great geological calendar, as given at p. 7, that he would scarcely date so far back as the commencement of the postpliocene period. CHAP. XIII. THE GLACIAL PERIOD. 229 CHAPTER XIII. CHRONOLOGICAL RELATIONS OF THE GLACIAL PERIOD AND THE EARLIEST SIGNS OF MAN'S APPEARANCE IN EUROPE. CHRONOLOGICAL RELATIONS OF THE CLOSE OF THE GLACIAL PERIOD AND THE EARLIEST GEOLOGICAL SIGNS OF THE APPEARANCE OF MAN EFFECTS OF GLACIERS AND ICEBERGS IN POLISHING AND SCORING ROCKS SCANDINAVIA ONCE ENCRUSTED WITH ICE LIKE GREENLAND — OUTWARD MOVEMENT OF CONTINENTAL ICE IN GREENLAND MILD CLIMATE OF GREENLAND IN THE MIOCENE PERIOD ERRATICS OF RECENT PERIOD IN SWEDEN GLACIAL STATE OF SWEDEN IN THE POSTPLIOCENE PERIOD -SCOTLAND FORMERLY ENCRUSTED WITH ICE-ITS SUBSEQUENT SUBMERGENCE AND RE-ELEVATION -LATEST CHANGES PRODUCED BY GLACIERS IN SCOTLAND REMAINS OF THE MAMMOTH AND REINDEER IN SCOTCH BOULDER CLAY-PARALLEL ROADS OF GLEN ROY FORMED IN GLACIER LAKES -COMPARATIVELY MODERN DATE OF THESE SHELVES. THE HE chronological relations of the human and glacial periods were frequently alluded to in the last chapter, and the sections obtained near Bedford (p. 164), and at Hoxne, in Suffolk (p. 168), and a general view of the Norfolk cliffs, have taught us that the earliest signs of Man's appearance in the British Isles, hitherto detected, are of post-glacial date, in the sense of being posterior to the grand submergence of England beneath the waters of the glacial sea. But after that period, during which nearly the whole of England North of the Thames and Bristol Channel lay submerged for ages, the bottom of the sea, loaded with mud and stones melted out of floating ice, was upheaved, and glaciers filled for a second time the valleys of many mountainous regions. We may now therefore inquire whether the peopling of Europe by the human race and by the mammoth and other mammalia 230 SUPERFICIAL TRACES OF THE EFFECTS CHAP. XIII. now extinct, was brought about during this concluding phase of the glacial epoch. Although it may be impossible in the present state of our knowledge to come to a positive conclusion on this head, I know of no inquiry better fitted to clear up our views respecting the geological state of the northern hemisphere at the time when the fabricators of the flint implements of the Amiens type flourished. I shall therefore now proceed to consider the chronological relations of that ancient people with the final retreat of the glaciers from the mountains of Scandinavia, Scotland, Wales, and Switzerland. Superficial Markings and Deposits left by Glaciers and In order fully to discuss this question, I must begin by referring to some of the newest theoretical opinions entertained on the glacial question. When treating of this subject in the Principles of Geology,' ch. xv., and in the 'Manual (or Elements) of Geology,' ch. xi., I have stated that the whole mass of the ice in a glacier is in constant motion, and that the blocks of stone detached from boundary precipices, and the mud and sand swept down by avalanches of snow, or by rain from the surrounding heights, are lodged upon the surface and slowly borne along in lengthened mounds, called in Switzerland moraines. These accumulations of rocky fragments and detrital matter are left at the termination of the glacier, where it melts in a confused heap called the 'terminal moraine,' which is unstratified, because all the blocks, large and small, as well as the sand and the finest mud, are carried to equal distances and quietly deposited in a confused mass without being subjected to the sorting power of running water, which would convey the finer materials farther than the coarser ones, and would produce, as the strength of the CHAP. XIII. PRODUCED BY GLACIERS AND ICEBERGS. 231 current varied from time to time in the same place, a stratified arrangement. In those regions where glaciers reach the sea, and where large masses of ice break off and float away, moraines, such as I have just alluded to, may be transported to indefinite distances, and may be deposited on the bottom of the sea wherever the ice happens to melt. If the liquefaction takes place when the berg has run aground and is stationary, and if there be no current, the heap of angular and rounded stones, mixed with sand and mud, may fall to the bottom in an unstratified form called 'till' in Scotland, and which has been shown in the last chapter to abound in the Norfolk cliffs; but should the action of a current intervene at certain points or at certain seasons, then the materials will be sorted as they fall, and arranged in layers according to their relative weight and size. Hence there will be passages from till to stratified clay, gravel, and sand. Some of the blocks of stone with which the surfaces of glaciers are loaded, falling occasionally through fissures in the ice, get fixed and frozen into the bottom of the moving mass, and are pushed along under it. In this position, being subjected to great pressure, they scoop out long rectilinear furrows or grooves parallel to each other on the subjacent solid rock. Smaller scratches and striæ are made on the polished surface by crystals or projecting edges of the hardest minerals, just as a diamond cuts glass. In all countries the fundamental rock on which the boulder formation reposes, if it consists of granite, gneiss, marble, or other hard stone capable of permanently retaining any superficial markings which may have been imprinted upon it, is smoothed or polished, and exhibits parallel striæ and furrows having a determinate direction. This prevailing direction, both in Europe and North America, is evidently connected with the course taken by the erratic blocks in the same dis 232 SCANDINAVIA ONCE ENCRUSTED CHAP. XIII. trict, and is very commonly from north to south, or if it be twenty or thirty or more degrees to the east or west of north, still always corresponds to the direction in which the large angular and rounded stones have travelled. These stones themselves also are often furrowed and scratched on more than one side, like those already spoken of as occurring in the glacial drift of Bedford (p. 165), and in that of Norfolk (pp. 213 and 218). When we contemplate the area which is now exposed to the abrading action of ice, or which is the receptacle of moraine matter thrown down from melting glaciers or bergs, we at once perceive that the submarine area is the most extensive of the two. The number of large icebergs which float annually to great distances in the northern and southern hemisphere is extremely great, and the quantity of stone and mud which they carry about with them enormous. Some floating islands of ice have been met with from two to five miles in length, and from one hundred to two hundred and twenty-five feet in height above water, the submerged portion, according to the weight of ice relatively to sea water, being from six to eight times more considerable than the part which is visible. Such masses, when they run aground on the bottom of the sea, must exert a prodigious mechanical power, and may polish and groove the subjacent rocks after the manner of glaciers on the land. Hence there will often be no small difficulty in distinguishing between the effects of the submarine and supramarine agency of ice. Scandinavia once covered with Ice, and a Centre of In the north of Europe, along the borders of the Baltic, where the boulder formation is continuous for hundreds of miles east and west, it has been long known that the erratic |