The term OOLITE or roestone, as applied to the whole of the groups enumerated above, is derived from the resemblance between the small rounded grains of which the limestones are generally composed, and the roe of a fish. The Jura mountains, which divide France from Switzerland, consist mainly of these deposits, and hence Jurassic—the _Terrains Jurrassiques_ of continental geologists. The word lias is simply a corruption of liers (layers), and has from time immemorial been applied to the rocks of this group. Their relation and order of superposition are fully brought out along the sections of the Great Western Railway from London to Bath. The Birmingham line from Derby by Rugby to the metropolis intersects nearly every member of the series, until they are covered about Wallingford by the chalk. When one looks at these innumerable bands of rock, and the great diversity of earthy matter of which they are composed, the mind becomes utterly overwhelmed by the rapidity and vastness of the changes which, during this epoch, occurred upon the surface of the globe. A turbid, and often agitated, condition of the waters in which they were deposited is very clearly indicated. The animals of the period were manifestly of a class peculiarly adapted to the impregnated element, the slimy banks, and shallows which prevailed. The flora was abundant, of a kind, and produced in circumstances, favorable for the formation of a lignite coal. The spasmodic action which prevailed after the deposition of the carboniferous beds had not entirely subsided at the Permian period. The change was of too violent a kind to have been brought about without great internal, as well as external, commotion. We find, accordingly, in most districts, that the rocks of this class are upturned and disrupted. The detritus of the new red sandstone and magnesian limestone, thereby occasioned, would go to form new land during the submergence of such portions of the surface as were retained beneath the waters. The oscillations were numerous and frequent, corresponding with the aggregate of beds which compose the system; while the quality and arrangement of the sediment point to changes and alterations in sea-levels, river courses, land boundaries, estuaries, the size and distribution of the basins into which the alluvia were transported. The geographic extent, combined with the frequently insulated position of the oolitic series, clearly demonstrates a vast alteration in the bed of the ocean, as well as in the ridges and elevations which gave diversity to the land. The oolites, in fact, constitute vast calcareous reefs, raised upon the inverted strata of the older formations, which formed the cliffs and headlands of a sea swarming with lizards and crocodilians, and over whose thick umbrageous banks roamed the flying pterodactyle, watching or perhaps escaping from, the singular saurians that reposed in the thickets beneath. The substitution of the pyritous clays for the saliferous marls;