Mineral Phosphates

Phosphatic nodules and concretions, with phosphatized fossils and their casts, occur at various geological horizons in Great Britain. Bands of black nodules, highly phosphatic, are found at the top of the Bala limestone in North Wales ; beds of concretions occur in the Jurassic series; and important deposits are known in the Cretaceous strata, especially in the Lower Greensand and at the base of the Gault. The Lower Greensand phosphates have been worked, under the name of "coprolites," at Potton in Bed fordshire and at Upware and Wicken in Cambridgeshire. The Cambridge Greensand, rich in phosphatic nodules, occurs at the base of the Chalk Marl. The chalk occasionally becomes phos phatized, as at Taplow (Bucks), Lewes (Sussex) and Ciply in Belgium. At the base of the Red Crag in East Anglia, and occa sionally at the base of the other Pliocene Crags, there is a "nodule bed," consisting of phosphatic nodules, with rolled teeth and bones, which were formerly worked as "coprolites" for the preparation of artificial manure. Lord Rayleigh has found that

phosphatized nodules and bones are rich in radioactive constit uents, and has brought this into relation with their geological age.

BIBLIOGRAPHY.-For

American phosphates see The Phosphates of America, by Francis Wyatt (5th ed., 1894) ; the Annual Reports on Mineral Resources of the U.S. (U.S. Geol. Survey), including some valuable reports by C. W. Hayes, also those in Rothwell's Mineral Industry; "Nature and Origin of Deposits of Phosphate of Lime," by R. A. F. Penrose, Jun., Bull. U.S. Geol. Survey, No. 46 (1888) ; Florida, South Carolina and Canadian Phosphates, by C. C. Hoyer Miller (1892) ; and The Non-metallic Minerals, by G. P. Merrill (19°4). Many of the above include descriptions of mineral phosphates in other parts of the world. For a general discussion of the origin of the phosphates, see "The Natural History of Phosphate Deposits," by J. J. H. Teall, Proc. Geol. Assoc., xvi. 369 (Igoo). Consult also Etude complete sur les phosphates, by A. Deckers (Liege, 5894).