In the study of glaciation and of other ancient climatic phenomena it has been tacitly assumed that changes of climate in the geological past have been due to causes which are not now in operation, or whose effects during the past few generations have been so small that they have escaped observation. This is a natural assumption. In the first place, the phenomena of the last Glacial period, which may serve as the standard example for all the main climatic changes, are so vastly greater than anything that we can now observe that the mind naturally supposes them to have been due to some cause of correspondingly grand proportions. In the second place, the phenomena of that period have appeared to be wholly different from anything now occurring. No one, for instance, has hitherto described any modern occurrences corresponding to the glacial accumulation of snow in Labrador and Scandinavia, . . .