on the nature of calcareous deposits, and on the contemporaneity of certain groups of deposits, dependent on the oscillatory movements of land and sea, the author described his plan of showing on maps the relative thicknesses of the two classes of strata under notice, by means of isodiametric or isometric lines (properly isopithic, or indicative of equal thickness of the strata).
Fig. 2.—Distribution of the Calcareous and Sedimeatary Strata of the Great Oolite, Oxfordshire.
Mr. Hull then proceeded to show the application of the isodiametric system of lines to the Carboniferous strata of the midland counties and north of England; showing that there is a south-easterly attenuation of the argillo-arenaceous strata, and a north-westerly attenuation of the calcareous strata. The existence, in the Carboniferous Period, of a barrier of land crossing the British area, immediately to the north of lat. 52°, was insisted upon; and, although this barrier was probably broken through (in South Warwickshire) in the latter portion of that period, yet it divided, in the author's opinion, the coal-area into a north and a south portion, the latter showing a very different set of directions in the attenuation of its strata; the shales and sandstones thinning out eastward and the limestones in the contrary direction.
In conclusion, the author stated his opinion that the source of the Carboniferous sediments was in the ancient North Atlantic Continent, for the existence of which Lyell, Godwin-Austen, and others have argued; and he inferred that the shores of this Atlantis, composed principally of granitoid or metamorphic rocks, were washed on the west side by a current running south-west which drifted the sediment in that direction; and, on the other, by a current running south-east which carried sediment over the submerged British area.
Geologists' Association.—February 3—Professor Tennant, F.G.S., President, in the chair. The following papers were read:—1. "On the Cretaceous Group in Norfolk." By C. B. Rose, Esq., F.G.S. The author, in an elaborate paper, described the general divisions of the chalk formation as exhibited in Norfolk, and following the arrangement proposed by the late Mr. Woodward, he divided the beds into Upper Chalk, Medial Chalk, Hard Chalk, and Chalk Marl. The Upper and Medial Chalk he stated to comprise the chalk with flints (the upper division of other geologists), and the author considers this distinction legitimate, inasmuch as the uppermost bed at Norwich contains organic forms which are not met with in the medial bed. The distinguishing characteristics of the several beds with their peculiar fossils, and the local limits of each formation were fully described, and the paper was illustrated by an elaborate section of the strata of the county.
2. "On the Plasticity and Odour of Clay." By C. Tomlinson, Esq. The author pointed out some of the most remarkable considerations in relation to this subject, such for instance as the fact that clay is only plastic up to a certain temperature; when heated beyond that point (which the author believes, from experiments performed by him, to be somewhere be-
