It is somewhat remarkable that, just as physicists are assuring geologists that the latter will have to quicken their forces, so as to bring the geological history of the globe within the definite limits assigned by the physicists themselves, the geologists reply by adding several thousand feet more rock in various parts of the world to the already thick column of sediment, and many would assure us that these ‘Archœan’ rocks were produced in a manner similar to the fossiliferous rocks, from which they differ in such important particulars.