[From the Report of the British Association/or the Advancement </ Science for 1875.] SERftAKAJ&M NOTES FREIBEfi&. ON THE CLASSIFICATION OF THE SEDIMENTAHY ROCKS. BY T. M'K. HUGHES, M.A., F.S.A., F.G.S., IVOODWARDIAN PROFESSOR OF GE()LOOY, CAMBRIDGE. Prof. Hughes, in advocating a revision of the classification of the sedimentary rocks, pointed out:—■ (1) That, although the accumulation of rock-material may have been going on somewhere throughout the whole of the periods with which geologists have to do, still that deposition has been locally interrupted many times ; (2) That the whole evidence had to be considered in each case, as it was a matter of every-day observation that trifling geographical changes might produce con siderable alteration not only in the character of the sediment, but also in the fauna and flora of a given area; and small local irregularities, due for instance to volcanic action, might produce phenomena which alone would be taken for an unconformity, implying a long interruption of deposit; (3) That denudation proves a lapse of time somewhat commensurate with the deposition of a similar thickness of material to that denuded. Bearing these principles in mind, he observed that the great divisions should be drawn where it can be shown there was the greatest and longest interruption in the continuity of conditions, the minor subdivisions being founded upon more rapidly varying circumstances, which often produce even greater difference in litho logical character and fossil contents. He pointed out that our present classification was very inconsistent—some of the breaks within the Primary, for example, being far more important than that between the Primary and Secondary rocks themselves. He proposed the following classihcation, read in ascending order:— 1st Epoch. 2nd v 3rd 4th 5 th » Laurentian. Gap. Labrador Series. Gap. Huronian ? > Pre- Cambrian. The Huronian he felt to be not quite well defined, but thought it probable that
