I. THE NATURE OF THE ROCKS. The oolitic or Jurassic system, like that of the new red sandstone, comprises the subdivisions of two well-marked natural groups, in which the lias or lower series is included. In point of geographical range, the oolite formation is extensively distributed over the surface of the globe; in mineral character it is varied in every possible degree of texture and composition; in geognostic arrangement there are intercalations, without end, of marine and terrestrial detritus; the organic remains are in the greatest profusion, both as to diversity of type and increase of new creations; and, locally, such has been the appreciation of its various members, that there is scarcely a town or parish in the south-eastern part of England, that has not received from or given habitations and name to, some one of its numerous subdivisions. Resting upon the triassic formation, there are bands of lias shales, limestones, sandy and ferruginous strata, and upper shales, including nodular concretions and beds of limestone. This series is distributed over the counties of York, Northampton, Somerset, and Dorset. The next are the lower oolites, which comprise an extensive series of calcareous, concretionary sands and sandstones, limestone, thin seams of coal and ligneous clays, and the Cornbrash limestone, which in many localities is a mere aggregation of shells and other marine exuviæ. The Stonesfield slate, the Forest marble, and the Fuller’s earth beds, are included in the group, ranging along the Yorkshire coast, through Northampton, Oxford, and Gloucester shires; and in Scotland we have their equivalents in the Brora coal and oolitic limestone of Sutherlandshire, Skye, and the adjacent islands. The middle oolite succeeds, which includes the Oxford clay, the Kelloway rock, and the coral-rag, all more or less distinguished by their profusion and peculiarity of fossils, chiefly shells, echini, and corals. The whole formation terminates in two well known deposits, the Kimmeridge clay and Portland oolite, with its bands of green and red sands, layers of chert and drift-wood. This group prevails in Oxfordshire, Berks, Wilts, Bucks, and the Isle of Portland; the matrix of fossilized reptilia, fishes, and cycadeous plants.