2. The _Middle Lias_, commonly known as the Marlstone, is surmounted by a bed of oolitic ironstone, largely worked in Leicestershire and in the north of England as a valuable ore of iron. The underlying marls and sands, the latter of which become somewhat argillaceous below, form beds from 200 to 300 feet thick in Dorsetshire and Gloucestershire; the fossils are _Ammonites margaritaceus_, _A. spinatus_, _Belemnites tripartitus_. The upper rock-beds, especially the bed of ironstone on the top, is generally remarkably rich in fossils. [Illustration: Fig. 88.--Gryphæa incurva.] 3. _Lower Lias_ (averaging from 600 to 900 feet in thickness) consists, in the lower part, of thin layers of bluish argillaceous limestone, alternating with shales and clays; the whole overlaid by the blue clay of which the lower member of the Liassic group usually consists. This member of the series is well developed in Yorkshire, at Lyme Regis and Charmouth in Dorsetshire, and generally over the South-West and Midland Counties of England. _Gryphæa incurva_ (Fig. 88), with sandy bands, occurs at the base, in addition to which we find _Ammonites planorbis Bucklandi_, _A. Ostrea liassica_, _Lima gigantea_, _Ammonites Bucklandi_, &c., in the lower limestones and shales. Above the clay are yellow sands from 100 to 200 feet thick, underlying the limestone of the Inferior Oolite. These sands were, until lately, considered to belong to the latter formation--as they undoubtedly do physically--until they were shown, by Dr. Thomas Wright, of Cheltenham, to be more nearly allied, by their fossils, to the Lias below than to the Inferior Oolite above, into which they form the passage-beds. In France the Lias abounds in the Calvados, in Burgundy, Lorraine, Normandy, and the Lyonnais. In the Vosges and Luxembourg, M. Elie de Beaumont states that the Lias containing _Gryphæa incurva_ and _Lima gigantea_, and some other marine fossils, becomes arenaceous; and around the Harz mountains, in Westphalia and Bavaria, in its lower parts the formation is sandy, and is sometimes a good building-stone.