THE imagination of Goethe pictured the ice-age. " If a great cold," said he, " covered the larger part of North Germany with ice, when the water was of the depth of 1,000 ft., one can imagine that the collision of masses of ice would cause great destruction; and storms coming from the north-west and the east would carry icebergs with blocks on them further south." In another place also he recognises a submergence and a still greater extension of ice, for, after rejecting the theory of a violent transportation of the erratic blocks in Savoy and Switzerland, he says :— " There was a period of groat cold when the sea covered the continent to a depth of 1,000 ft., and the Lake of Geneva was in communication with the North Sea. The glaciers of Savoy descended much lower than now, and the moraines and long lines of boulders extended as far as the valley of the Arve and the Drones, where the rocks were transported with their angles intact."
He goes on to the glacier theory in another passage :— " Finally, two or three quiet guests called to their aid a period of intense cold, and saw in their minds'-eye glaciers descending from the highest mountain like gliding roads, far into the low country, upon which, as on an inclined plane, heavy primary blocks were slid forward and further onwards. So that, at the period of thawing of the ice, they sank down and remained per- manently on the foreign soil."
It is generally allowed that there was an enormous exten- sion of ice at a not very remote period over North-Western Europe and North-Eastern America; but our author brings forward abundant evidence to show that similar conditions * The Glacial Nightmare and the Flood, a Second Appeal to Common-Senee from the Extravagance of some Recent Geology. By Sir Henry H. Howorth, KALE , M.P., F.R.S., &o. London: Sampson Low and Co, 1893. did not extend along Northern Asia, and could not be con- sidered in any way circumpolar. Ho gives references to the writings of travellers and navigators to prove that the North Pole is not, and never was likely to have been, the centre of greatest cold or of ice-dispersal; and that, although in the Southern Hemisphere also there are traces of the former greater extension of glaciers in the mountain districts, there is nothing to show anything like widespread oircumpolar glaciation, or even any creeping of the ice north over the known glaciated areas from Antarctic regions. These are points of the first importance in considering the question whether the greater extension of ice in what is called the " Glacial Epoch" must be referred to cosmical causes—such as the coincidence of the extreme obliquity of the ecliptic with the extreme eccentricity of the earth's orbit, with all the accompanying difference in the duration of summer and winter, and other climate-affecting conditions—or whether, on the other band, the phenomena may not be more easily explained by referring them to geographical changes, such as the upheaval of large masses of land, so as to deflect the ocean currents, and the elevation of mountain-ranges to such a height that snowfields and glaciers, or even ice-sheets, would necessarily be formed in the districts where the traces of ancient ice-action are now observed.
At the very first step, we find fundamental differences of opinion, both as to the facts and as to the explanations. If we inquire what the traces are which it is desired to explain, we learn that they cannot possibly be referred to one and the same operation. Shells cannot, for instance, have lived on a sea-bed when it was filled with solid ice. Stratified drift and boulder-clay must each have bad a different origin. And it is difficult to understand how blocks could be picked up from the bed of an ice-sheet ; for, if the ice was there, the rocks could be only at the temperature of the bottom of a glacier, and could not be broken up by frost; and if the ice was not there, they could not be removed if loosened.
Again, the chief difficulty in the way of our acceptance of the theory of the glacial erosion of lake-basins, is that they do not occur where they should on that hypothesis. But we have not room to dwell longer on this interesting question.
Then, looking at the possible agents, we know that glacier- ice does push along vast masses of broken rock ; icebergs do carry and drop what they had on them and in them as they started on their voyage from the ice-foot ; torrents and sea- currents do transport sand and shingle and masses of rock. The question is, to which of these forces, or to what combina- tion of them, may we, with greatest probability, refer any particular mass of drift P and how may we best account for any set of groovings or etrh33 on the face of the solid rock P Having regard to the results also, there is no doubt that we have marine drifts and drifts due to the water in, under, and at the foot of the glaciers ; we have iceberg-drift, and drift carried on and in land-ice ; and all these involve different' local conditions.
Several ingenious explanations have been offered of the occurrence of marine shells in stratified drift at various levels on the flanks and tops of the mountains and hills in Southern Sweden, in Northern England, Wales, and elsewhere. The more obvious explanation is, that they were left there in the shingly beach of the receding post-glacial sea. But this was chiefly objected to because it would have involved earth-move- ments in comparatively recent times to so great an extent as would lend probability to the theories of elevations such as would account for glaciers in temperate regions, and sub- mergenoes such as would explain the widespread post-glacial Bands and gravels.
Some, therefore, suggested that these masses had been scraped up from the sea-bottom, and pushed bodily up the mountains to their present position ; that they were, in fact, part of the terminal moraine of the polar ice-sheet. The difficulty of explaining the even stratification, and the ripple- marks on the beds, as well as the non-Arctic character of the shells, did occur to many, and some got over it by supposing that the shells were pushed up in front of the ice from the sea-bed in temperate regions, but that the deposit in which they are now seen was washed from the ice-foot at these several elevations by the fresh water, due to the melting of the ice, bearing away with it the mud, sand, and stones trans- ported so far by the ice-sheet.
Thus, we are led on to consider, in not one but many instances, whether the phenomena require, to use our author's favourite philosophical term, some transcendental cause ; or whether, when we admit that Nature is perpetually shifting the scene of greatest activity, these apparently exceptional eases may not be brought under her ordinary operations. Looking over the applications of the astronomical theory of vicissitudes of climate, we cannot but have our confidence shaken by the irreconcilable difference of opinion which exists among its supporters as to its direct, and still more as to its indirect, effects. To give one example,—Croll thought that the hemisphere of cold winter would be the glaciated one ; Murphy, on the other hand, was of opinion that the hemi- sphere of cool summer would be that which is glaciated.
Another point which must be settled, before what we may call the "astronomical theory of glaciation" is accepted, is whether or not the phenomena are contemporaneous over the whole of one hemisphere, and whether or not they are alter- nate in each hemisphere. There would be nothing remark- able in the general synchronism of the great earth-movements round the North Atlantic basin ; and our author offers much testimony in favour of the limitation of extreme glacial phe- nomena to that area,—a fact easily explained by reference to geographical conditions. But there is no good evidence for the occurrence at any time of glacial conditions all over the polar and temperate regions of either hemisphere, nor for the recurrence of widespread glaciation over a similar area during the deposition of any of the older formations, though moun- tain-ranges with sufficient snow to give rise to glaciers probably did often exist and did produce them. Nor is there evidence among the results of the last time of extreme cold along the Atlantic borders, of interglacial periods affect- ing the whole glaciated area. Local glaciation in Tertiary and still earlier ages in the vicinity of great mountain-ranges such as the Alps and Himalayas, is quite consistent with the view that earth-movements were not continuous in one direc- tion, but oscillated, so as to give rise to the advance and recession of glaciers or ice-sheets.
These matters have been fully discussed by Gur author, who has been very successful in formulating the real questions at issue, and in separating the proved from the unproved, and the unproved from the disproved, points in the case. We must, however, be careful, while protesting against the exaggeration of the extreme glacialists, that we do not reject too much, or urge equally extreme applications of our own theories instead.
Our author has been ill-advised in his choice of a title. It is irritating to those against whose views he sums up, to describe their theory as a nightmare, even though it may turn out to be the result of undigested facts ; while his always speaking of the flood has a tendency to estrange many who agree with him in believing that there was a great sub- mergence, which, they hold, commenced in later glacial times, and helped much to lift the ice-shroud off the Atlantic border. lands, though they may not go so far as he does in respect of its sudden and transient nature.
It does seem to have been forced on the minds of many observers, that much of the drift must be referred to the more or less violent action of currents of water. Dien Dr. James Geikie, who cannot be accused of leaning to the views of our author, expresses himself almost as strongly as he would in respect of the distribution of the gravelly drift, only he refers it, not to marine action, but to the fresh-water from the foot of the ice-sheet. He says, in his sketch of the history of the Cheviot Hills : " In the regions south of the Humber, we find the country often sprinkled with tumultuous heaps and wide. spread sheets of gravel and brick-earth, which seem to owe their origin to the floods and torrents that escaped from the melting ice. These waters, sweeping over the land, carried along with them such relics of man and beast as lay at the surface, washing away interglacial river-deposits, and scat- tering the materials far and wide over the undulating low- grounds of Eastern and Central England."
If there are any who do not want to be troubled with the reasons and authority for every statement, this is not the book for them. If there are any who believe so strongly in their own infallibility that the mere questioning of what they have declared to be their opinion is an impertinence, and who insist that their shibboleth must be pronounced on pain of exclusion from the circle of those who know, our author is too fearless a critic to please them. If there are any who have staked too heavily on their fallacies escaping detection, and on the small memory the public has for previous positive state- ments, to like to have the whole question reopened, it cannot be denied that to them this book may bring an uneasy feeling. But it will be welcomed by those who like to examine from time to time the basement upon which they are raising a vast superstructure, on every part of which new extensions will probably be carried out,—by those who realise that the glacial theories are one and all based on circumstantial evidence, and that each link in the chain is itself a large theory similarly built up. Our author is as fair in statement and skilful in exposition as he is unsparing in labour and fertile in resource, and there is good strong common-sense apparent throughout the work. It can hardly be called an interesting book for the general reader, not because it is couched in technical language unintelligible to any but specialists, but because it consists of a vast mass of compressed facts and opinions. Yet it is a very readable book for any one who wants to know about the various views which have been propounded on the subject treated of. To all students of glacial phenomena it will be simply indispensable.