February 8, 1871.
The following communications were read : —
1. On the Punfield Formation. By John W. Judd, Esq., F.G.S., of the Geological Survey of England.
Contents.
I. Introduction. II. Bibliography of the subject. III. Sections in the Isle of Purbeck. 1. Punfield Cove. 2. Worborrow Bay. 3. Mewps Bay. 4. Lulworth Cove. IV. Sections in the Isle of Wight. 1. Brixton Bay. 2. Compton Bay. 3. Sandown Bay. V. Sections in the Weald of Sussex, Surrey, and Kent. h Leith Hill, near Guildford. 2. Hythe. VI. Relations of the Punfield Formation to the Wealden, Neocomian, and Cretaceous of the south of England. 1. Unconformity between the Cretaceous and Neocomian. 2. Variation in character of the Cretaceous, in proceeding from east to west. 3. Thinning-out westward of the Neocomian and Wealden. 4. Relation of the Purbeck to tbe Wealden. VII. Foreign equivalents of the Punfield Formation. 1. Urgonien and Rhodanien of France, Switzerland, &c. 2. Coal-bearing strata of eastern Spain. VIII. Conclusion. I. Introduction. The existing scheme of classification of geological formations is in the main founded on the study of marine strata only. The circumstance that rocks of freshwater and terrestrial origin occupy much smaller areas than those of marine character, doubtless in part accounts for this result, which, however, is to a much greater extent attributable to the fact that the fossils of the former class of strata are much less numerous and less strikingly characterized than those of the latter. With the progress of geological research and its gradual extension over wider areas, the necessity for successive enlargements and modifications of our scale of geological periods has from time to time become manifest. The conclusion, so strongly insisted upon by Mr. Darwin and Professor Ramsay, that unconformities between strata indicate the lapse of enormous periods of time, is being constantly confirmed by the discovery, as fresh districts come under investigation, or old ones are more accurately studied, of formations which more or less completely represent these "breaks." Not less important in its bearing upon geological theory is the fact that old and well-known formations, as they are studied at points more and more remote from the typical district, exhibit new cha- q2
