Some Salient Points in the Science of the Earth

by Sir John William Dawson

The late Prof. Alexander Winchell, a man who did not hesitate to express his convictions, thus bears similar testimony:—"There has been no continental glacier. There has been no uniform southerly movement of glacier masses. There has been no persistent declivity as a sine qua non, down which glacier movements have taken place. The continuity of the supposed continental glacier was interrupted in the regions of the dry and treeless plains of the west; and in the interior and Pacific belts of the continent within the United States, ancient glaciation was restricted to the elevated slopes."[170] He might have added that the St. Lawrence valley was submerged and received the ends of Appalachian and Adirondack glaciers on the south-east, and those of Laurentide glaciers on the north-west.

[170] Nov., 1890.

My friend Prof. Claypole, who, however, has some hesitation, fearing, I presume, to be cast out of the synagogue for heresy, ventures to say,[171] "We deduce from the facts and arguments stated above, that all the observations of glacial action in the northern hemisphere are explicable by assuming the existence of enormous and confluent[172] glacier-systems in and about the high lands of Europe, Asia, and America, which high lands became, therefore, glacial radiants, and shed their load of ice in all directions over the lower adjacent ground, along the lines of easiest flow; that this theory does no violence to the analogy of the existing order of things, requiring merely an enlargement of actual glaciers by the intensification of actual conditions : that abundant evidence can be obtained, as, for example, from Switzerland, that the present glacier system of the earth was once of sufficient magnitude to produce all the observed phenomena; that the most important glacial radiants in the northern hemisphere were, in North America, the district round Hudson Bay, New England and the Adirondacks, with certain areas in the western Cordilleras, and in Europe the Norwegian Dovrefelds and the Alps, Asia apparently possessing none of commensurate importance; that it satisfactorily explains, also, the previously puzzling absence of glacial action over the great plain of Siberia, the coldest portion of the northern temperate zone; that the belief in a vast polar ice cap, thousands of feet thick, covering the whole Arctic region, and extending almost continuously down to low latitudes, is an assumption doing violence to observed physical facts and to probability, that it is not required to account for the phenomena, and is, in fact, contradictory to some of them."

[171] American Geologist, Feb., 1889.

[172] The term "confluent" is not necessary here. The glaciers of all mountain chains may be said to be more or less confluent in the nevé, from which individual glaciers radiate.

In Europe there is equally good evidence of the existence of huge glaciers on the Scandinavian mountains and the Alps, and of lesser accumulations of ice on the hills, as, for instance, those of the British Islands; but the Scandinavian boulders scattered over the plains of Great Britain must have been water-borne.[173]

[173] The reports of the Scottish boulder committee, and Lapworth's recent careful examination of the deposits on the East of England (Journ. Geol. Soc., Aug., 1891), strongly confirm me in this opinion.

In connection with these extracts I would observe that the writer, and those with whom he has acted in this matter, have never held that icebergs alone, or fields of ice alone, have produced the Pleistocene deposits. Their contention has been that the period was one in which glaciers, icebergs, and field ice acted together, and along with aqueous agencies, in producing the complicated formations of this remarkable age. They have, however, objected strenuously to the sole employment of one agent to the exclusion of others, and to attributing to that agent powers and extension which obviously could not belong to it, under the known laws which regulate the movement of glaciers by the force of gravity, and the precipitation of moisture in the form of snow on mountains and plateaus. These laws show that the movement of glaciers over level surfaces, or against the slope of the ground, and their moving stones otherwise than down slopes, are physical impossibilities, and that the accumulation of snow to form glaciers can take place only on elevated and cold land, supplied with large quantities of vapour from neighbouring water. Such accumulation can under no imaginable conditions take place in the interior plains and table lands of great continents.

Applying these laws and conclusions to the whole northern hemisphere, we learn that the conditions to produce a glacial period are the diversion of the warm currents from the northern seas, the submergence of land in the temperate regions, and its invasion by cold Arctic water, and great condensation of snow on the higher lands. Whether this condensation has a tendency finally to rectify the state of affairs, by pressing down the mountains and elevating the plains, we do not know, but I should imagine that it has not; for the high lands will, in the case supposed, be lightened by denudation, while the plains will be burdened with a great weight of deposit. Perhaps we should rather look to this as the agency for depressing and submerging the plains and elevating the hills, and suppose some other and more general pressure proceeding from the great sea basins, to effect the re-elevation of the plains.

These questions suggest that of the date of the Glacial period. This subject has recently been discussed by Prestwich and others, with the result that there is no purely geological ground for referring the Glacial age to a period so remote as that advocated by Croll on astronomical grounds. Claypole has recently discussed the matter at some length, and in a temperate spirit.[174] He takes the rate of erosion of the Niagara gorge as a measure, and shows that the Falls of St. Anthony, as described by Winchell, and all the other falls and river gorges in North America, give similar estimates, which are confirmed by the evidences of lake ridges, of the rate of erosion, and of the conditions of animal and plant life. The whole go to show that the culmination of the Glacial age may have occurred less than 10,000 years ago. He further shows that the differential elevation of Lakes Erie and Ontario, the greater ease with which the river could cut the lower part of its ravine, the probability that the part of the gorge between the whirlpool and the fall was not cut, but only cleaned out in modern times, and the possible greater flow of water in the early modern period, all tend to shorten the time required, and that, as Prestwich has inferred from other data, and the writer also in various papers, some of them of old date, the so-called post-glacial period, that of the melting away of the ice, may come within 8,000 to 10,000 years of our own time. Probably the first of these figures is the nearest to the truth,[175] so that, geologically considered, the Glacial age is very recent.