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Updated: May 18, 2025
Even in that case, however, it is difficult not to suppose that the Glen Roy country participated in the downward movement which sank part of Lanarkshire 525 feet beneath the sea, subsequently to the first great glaciation of Scotland.
In like manner the glaciation although identical in kind is on so small a scale in the existing Alpine glaciers as at first sight to disappoint a Swedish, Scotch, Welsh, or North American geologist.
My speculation was based upon the former glaciation of the northern temperate zone, and the inference of a warmer period preceding and perhaps following.
Natural as it may seem to look for exceeding cold as the cause of glaciation, the facts show us that we can not hold this view.
Once, indeed, in the Permian Age, all over the temperate regions, north and south, we get passing indications of what seems very like a glacial epoch, partially comparable to that great glaciation on whose last fringe we still abide to-day.
Thus the most evident cause of glaciation must be sought in those alterations of the land which affect the movement of the oceanic currents. Applying this principle to the northern hemisphere, we can in a way imagine a change which would probably bring about a return of such an ice period as that from which the boreal realm is now escaping.
Many a water-shed may intervene between the starting-point of each erratic or pebble and its final resting- place, and the only means of discovering the country from which it took its departure will consist in a careful comparison of its mineral or fossil contents with those of the parent rocks. Glaciation of Scandinavia and Russia. Glaciation of Scotland. Mammoth in Scotch Till.
Upheaval is the one constant and clearly recognisable feature associated with, or preceding, ice-ages. We saw this in the case of the Cambrian, Permian, Eocene, and Pleistocene periods of cold, and may add that there are traces of a rise of mountains before the glaciation of which we find traces in the middle of the Archaean Era.
For after the glaciation north comes the glaciation south, and unless our cold temperate zone were pushed down beyond the geographical equator, none of its living forms could ever have reached the corresponding zone in the southern hemisphere.
One condition of glaciation in the coincidence of winter with the maximum of remoteness from the sun, is present; the other a high eccentricity is deficient. Yet the ring of ice-bound territory hemming in the southern pole is well known to be far more extensive than the corresponding region in the north.
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