The study of the earliest fossiliferous rocks, as well as that of their animal remains, has been, and will be for a long time to come, a subject of very considerable interest, and one that has, especially during the last few years, attracted the keen attention of several experienced and conscientious observers. Many have been the observations assembled in connection with the direct order of superposition and relative age of the various rocks composing the Cambrian and Lowest Silurian deposits, as well as in seeking out all the data that could be obtained, so as to enable the palæontologist to attempt a correct diagnosis of the very earliest known ancestors of many of our fossils. The discoveries effected by Sir W. Logan amongst the ‘Laurentian’ rocks of North America (as stated by Sir R. I. Murchison) “constitute the foundation stones of all Paæeozoic deposits in the crust of the globe wherever their formations are known;” and with what keen interest has not the Eozoon been welcomed and elaborated—the oldest animal known!