+-----+------------------------------+-------------------+--------------------------+-------------------------------+ | | S. W. England and Midlands. | Yorkshire. | Ammonite Zones.* | Divisions according to | | | | | | A. de Lapparent.** | +-----+------------------------------+-------------------+--------------------------+-------------------------------+ | U L | Midford Sands (passage beds) | Alum shale |_Am. jurensis_ \ | (Including the _opalinus_ zone| | p i | | | | | of the Inferior Oolite.) | | p a | Clays with Cement-stones | Jet Rock | " _communis_ > U. | Toarcien. | | e s | Limestones and Clays | Grey Shale | " _serpentinus_ / | | | r . | | | " _annulatus_ \ | | +-----+------------------------------+-------------------+------------------- | ---+-------------------------------+ | M | | | | | | | i L | Marlstone and Sands | Ironstone Series |_Am. spinatus_ | | | | d i | (Rock Bed and Ironstones) | | | | | | d a | Micaceous Clays and Sands | Sandy Series | " _margaritatus_ | | | | l s | | | | | | | e . | | | > M. | | +-----+------------------------------+------------------ +------------------- | | Charmouthien. | and | | Clays with occasional bands | Upper Series with |_Am. capricornus_ | | | | | of Limestone | Ironstone nodules| " _Jamesoni_ | | | | L L | | | and | | | | o i | | | " _armatus_ / | | | w a | | | +-------------------------------+ | e s | Limestones and Clays | Lower Series with | " _oxynotus_ \ | | | r . | | Sandy and Marly | " _Bucklandi_ > L. | Sinémourien. | | | | Beds | " _angulatus_ | | Hettangien including "White | | | | | " _planorbis_ / | Lias." | +-----+------------------------------+-------------------+--------------------------+-------------------------------+ | | | | | Rhétien. | +-----+------------------------------+-------------------+--------------------------+-------------------------------+ * The brackets indicate the divisions made by R. Tate and J. F. Blake. ** _Traité de géologie_ (5th ed., Paris, 1906).
The economic products of the Lias are of considerable importance. In the Lower Lias of Lincolnshire and the Middle Lias of Oxfordshire, Northamptonshire, Lincolnshire, Leicestershire and Yorkshire the beds of ironstone are of great value. Most of these ores are limestones that have been converted into iron carbonate with some admixture of silicates; they weather near the surface into hydrated peroxide. At Frodingham in Lincolnshire the oolitic iron ore reaches 30 ft. in thickness, of which 12 ft. are workable. In Gloucestershire the top beds of the Lower Lias and lower beds of the Middle division are the most ferruginous; the best ores near Woodstock and Banbury and between Market Harborough and Leicester are at the summit of the Middle Lias in the Marlstone or Rock bed. The ironstone of Fawler is sometimes known as Blenheim ore. The ores of the Cleveland district in Yorkshire have a great reputation; the main seam is 11 ft. thick at Eston, where it rests directly upon the Pecten Seam, the two together aggregating 15 ft. 6 in. Similar iron ores of this age are worked at Meurthe-et-Moselle, Villerupt, Marbache, Longuy, Champagneulles, &c. Some of the Liassic limestones are used as building stones, the more important ones being the Lower Lias Sutton stone of Glamorganshire and Middle Lias Hornton stone, the best of the Lias building stones, from Edge Hill. The limestones are often used for paving. The limestones of the Lower Lias are much used for the production of hydraulic cement and "Blue Lias" lime at Rugby, Barrow-on-Soar, Barnstone, Lyme Regis, Abertham and many other places. Roman cement has been made from the nodules in the Upper Lias of Yorkshire; alum is obtained from the same horizon. A considerable trade was formerly done in jet, the best quality being obtained from the "Serpentinus" beds, but "bastard" or soft jet is found in many of the other strata in the Yorkshire Lias. Both Lower and Upper Lias clays have been used in making bricks and tiles.