Mr. James Croll, in a letter to "Nature" (July 13, 1876), incidentally mentions the lessons that may be derived from the configurations of the earth's surface.
"Given the hardly perceptible wearing of water and time, a cañon a mile deep, and many hundreds of miles long, has resulted from the flowing of a stream. Given glacial 'abrasion' and time enough, then valleys of rounded section and firths and lake-basins of a particular kind probably resulted from the flowing of ice.
"Where a stream flows from source to mouth on a gradual slope, there has been no great disturbance of level since the stream began to work. Where ice fills the dales there are no cañons. Where ice has filled dales and has left fresh marks, cañons are short and small. In mountain regions, where ice-marks are rare or absent, cañons are of great depth and length, apparently because their streams have flowed in the same channels ever since the mountains were raised. But where cañons are marked features, these lakes, firths, and dales of rounded section are very rare, or do not exist. It seems therefore that hollows which have, in fact, been carved out of the earth's surface may be known for water-work or for ice-work by their shape, and that firths, dales, and lakes may mark the sites of local glacial periods; and cañons the sites of climates that have not been glacial since the streams began to flow."
One of the problems which geologists now propose to themselves is to ascertain definitely whether the existence of man before the close of the glacial epoch can be certainly proved. The method of proof consists in the examination of formations older than those of that epoch, in the hope of finding in them bones or implements of human origin. Mr. S. B. J. Skertchly thinks he has done this. In the valley sides around the town of Brandon, in England, "are preserved patches of brick-earth, which are valuable as affording the only workable clay in the district. Whenever these beds are well exposed they are seen to underlie the chalky boulder-clay of glacial age. Of this there cannot be the slightest doubt, for the glacial bed is typically developed and not in the slightest degree reconstructed. In these beds I have been so fortunate as to find palæolithic implements in two places; and in one of them quantities of broken bones and a few fresh-water shells. The implements are of the oval type, boldly chipped, but without any of the finer work which distinguishes the better made palæolithic implements. Although it would be rash to lay too great a stress upon the characters of these implements, it is nevertheless worthy of remark that they do belong to the crudest type. Equally rough specimens are found in the gravels above the boulder-clay, and even among neolithic finds. Still these very antique implements certainly do seem to belong to an earlier stage of civilization, if we regard them as examples of the best workmanship of their makers." These, he thinks, are the oldest specimens of man's handiwork known, and prove him to have lived before the culmination of the glacial epoch.