Man and the Glacial Period

by G. Frederick Wright

Connected with these terrace gravels in northern France is a loamy deposit, corresponding to the loess in other parts of Europe, and to a similar deposit to which we have referred in describing the southwestern part of the glaciated area in North America. In northern France this fine silt overlies the high-level gravel deposits, and, as Mr. Prestwich has pretty clearly shown, was deposited contemporaneously with them during the early inundations and before the stream had eroded its channel to its present level.

The distribution of loess in Europe was doubtless connected with the peculiar glacial conditions of the continent. Its typical development is in the valley of the Rhine, where it is described by Professor James Geikie “as a yellow or pale greyish-brown, fine-grained, and more or less homogeneous, consistent, non-plastic loam, consisting of an intimate admixture of clay and carbonate of lime. It is frequently minutely perforated by long, vertical, root-like tubes which are lined with carbonate of lime—a structure which imparts to the loess a strong tendency to cleave or divide in vertical planes. Thus it usually presents upright bluffs or cliffs upon the margins of streams and rivers which intersect it. Very often it contains concretions or nodules of irregular form.... Land-shells and the remains of land animals are the most common fossils of the loess, but occasionally fresh-water shells and the bones of fresh-water fish occur.”

“From the margins of the modern alluvial flats which form the bottoms of the valleys it rises to a height of 200 or 300 feet above the streams—sweeping up the slopes of the valleys, and imparting a rich productiveness to many districts which would otherwise be comparatively unfruitful. From the Rhienthal itself it extends into all the tributary valleys—those of the Neckar, the Main, the Lahn, the Moselle, and the Meuse, being more or less abundantly charged with it. It spreads, in short, like a great winding-sheet over the country—lying thickly in the valleys and dying off upon the higher slopes and plateaux. Wide and deep accumulations appear likewise in the Rhône Valley, as also in several other river-valleys of France, as in those of the Seine, the Saône, and the Garonne, and the same is the case with many of the valleys of middle Germany, such as those of the Fulda, the Werra, the Weser, and the upper reaches of the great basin of the Elbe. It must not be supposed that the loess is restricted to valleys and depressions in the surface of the ground.

“It is true that it attains in these its greatest thickness, but extensive accumulations may often be followed far into the intermediate hilly districts and over the neighbouring plateaux. Thus the Odenwald, the Taunus, the Vogelgebirge, and other upland tracts, are cloaked with loess up to a considerable height. Crossing into the drainage system of the Danube, we find that this large river and many of its tributaries flow through vast tracts of loess. Lower Bavaria is thickly coated with it, and it attains a great development in Bohemia, Upper and Lower Austria, and Moravia—in the latter country rising to an elevation of 1,300 feet. It is equally abundant in Hungary, Galicia, Bukowina, and Transylvania. From the Danubian flat lands and the low grounds of Galicia it stretches into the valleys of the Carpathians, up to heights of 800 and 2,000 feet. In some cases it goes even higher—namely, to 3,000 feet, according to Zeuschner, and to 4,000 or 5,000 feet, according to Korzistka. These last great elevations, it will be understood, are in the upper valleys of the northern Carpathians. In Roumania loess is likewise plentiful, but it has not been observed south of the Balkans. East of the Carpathians—that is to say, in the regions watered by the Dniester, the Dnieper, and the Don—loess appears also to be wanting, and to be represented by those great steppe-deposits which are known as Tchernozen, or black earth.”[BW]

[BW] Prehistoric Europe, pp. 144-146.

The shells found in the loess indicate both a colder and a wetter climate during its deposition than that which now exists. The relics of land animals are infrequently found in the deposit, yet they do occur, but mostly in fragmentary condition—the principal animals represented being the mammoth, the rhinoceros, the reindeer, and the horse; which is about the same variety as is found in the gravel deposits of the Glacial period, both in western Europe and in America.

A species of loess—differing, however, somewhat in color from that on the Rhine—covers the plains of northeastern France up to an elevation of 700 feet above the the sea, where, as we have already said, it overlies the high-level gravels of the Seine and the Somme. Above this height the superficial soil in France is evidently merely the decomposed upper surface of the native rock.

The probable explanation of all these deposits, included under the term “loess,” is the same as that already given by Prestwich of the loamy deposits of northern France. But in case of rivers, which, like the Rhine, encountered the ice-front in their northward flow, a flooded condition favouring the accumulation of loess was doubtless promoted by the continental ice-barrier. In the case of the Danube and the Rhône, however, where there was a free outlet away from the glaciated region, the loess in the upper part of the valleys must have accumulated in connection with glacial floods quite similar to those which we have described as spreading over the imperfectly formed water-courses of the Mississippi basin during the close of the Ice age. That the typical loess is of glacial origin is pretty certainly shown, both by its distribution in front of glaciers and by its evident mechanical origin when studied under the microscope. It is, in short, the fine sediment which gives the milky whiteness to glacial rivers.