The lower valleys of the Pyrenees and other Spanish ranges show it well, and it is conspicuous likewise in northern Italy, especially over the low tracts at the mouths of the great lake-valleys. In all those places one can see boulder-clay of as pronounced a character as any to be met with in Scotland. Danish, Dutch, German, and Russian geologists have of late years devoted much attention to the study of this clay, which is so remarkably developed in their respective countries. It has been long well known that a large proportion of the stones and boulders contained in the till are of northern derivation, but it is only of recent years that we have ascertained the particular routes by which those wanderers or erratics have travelled. The rock-fragments in question have been tracked back, as it were, to their parent masses, and thus, partly in this way, and partly by the evidence of ice-worn surfaces, we have been enabled to follow the spoor of the great northern ice-sheet in a most satisfactory manner. Let one or two examples suffice. Boulders derived from Lapland and Finland occur in the till at St. Petersburg, and have been traced south-east to Moscow. Again, fragments carried from Gottland, in the Baltic, are met with in the boulder-clay of east Prussia, and have been followed south to beyond Berlin. In like manner boulders of well-known Scanian rocks appear in the boulder-clay of Leipzig. So also Swedish and Norwegian rock-fragments are seen in the boulder-clay of Denmark, Hanover, and Holland.