I have myself shewn that there are such centres of distribution in Scotland, and England, and Ireland; and these facts have been since traced in detail in various parts of the British islands by Dr Buckland, Sir Charles Lyell, Mr Darwin, Mr M'Laren, and Professor James Forbes, pointing clearly to the main mountain groups as to so many distinct centres of dispersion of these loose materials. Similar phenomena have been shewn in the Pyrenees, in the Black Forest, and in the Vosges, shewing beyond question, that whatever might have been the cause of the dispersion of erratic boulders, there are several separate centres of their distribution to be distinguished in Europe. But there is another question connected with this local distribution of boulders which requires particular investigation, the confusion of which with the former has no doubt greatly contributed to retard our real progress in understanding the general question of the distribution of erratics. It is well known that Northern Europe is strewed with boulders, extending over European Russia, Poland, Northern Germany, Holland, and Belgium. The origin of these boulders is far north in Norway, Sweden, Lapland, and Liefland; but they are now diffused over the extensive plains west of the Ural Mountains. Their arrangement, however, is such that they cannot be referred to one single point of origin, but only in a general way to the northern tracts of land which rise above the level of the sea in the arctic regions. Whether these boulders were transported by the same agency as those arising from distinct centres, on the main Continent of Europe, has been the chief point of discussion. For my own part, I have indeed no doubt that the extreme consequences to which we are naturally carried by admitting that ice was also the agent in transporting the northern erratics to their present positions, has been the chief objection to the view, that the Alpine boulders have been distributed by glaciers. It seemed easier to account for the distribution of the northern erratics by currents; and this view appearing satisfactory to those who supported it, they at once went further, and opposed the glacial theory even in those districts where the glaciers seemed to give a more natural and more satisfactory explanation of the phenomena. To embrace the whole question it should be ascertained: