The question of the origin of the Archæan rocks is one of such great interest that it will not be thought unimportant on the one hand to record any facts that may bear upon it, and on the other to examine somewhat severely all the evidence that may be from time to time brought forward on the subject. Among the facts which may be adduced in support of the view that the Archæan rocks are altered sedimentary strata, the occurrence of breccias and conglomerates may well claim a foremost place; and a vast amount of superincumbent theory must rest on a very shaky foundation if there be any doubt whether some of those ancient fragmental beds be true conglomerates or not. The manner of occurrence, the mode of formation, and the character of pseudo-breccias and pseudoconglomerates become therefore questions of first importance.