Bulletin of the United States Geological Survey--The Nature and Origin of Deposits of Phosphate and Lime . ules, while the content ofphosphoric acid in them may be widely different. All through the counties of Dorset, Somerset, Wilts, and Devon thenodules are very much more siliceous and less abundant than the nod-ules of Cambridgeshire and Besides the variability iothe phosphatic richness of the bed, it is also sometimes very variable inits mode of occurrence. At times it will cover many square miles con-tinuously, while at others it occurs iu pockets in the surface of tbeGault
Bulletin of the United States Geological Survey--The Nature and Origin of Deposits of Phosphate and Lime . ules, while the content ofphosphoric acid in them may be widely different. All through the counties of Dorset, Somerset, Wilts, and Devon thenodules are very much more siliceous and less abundant than the nod-ules of Cambridgeshire and Besides the variability iothe phosphatic richness of the bed, it is also sometimes very variable inits mode of occurrence. At times it will cover many square miles con-tinuously, while at others it occurs iu pockets in the surface of tbeGault. At other times, according to Mr. Fisher, the bed shows signsof contortion, as indicated in Fig. 34. It will be seen, by examining theanalyses given beyond, that the Greensand matrix of the phosphaiicnodules varies also very much in its content of phosphoric acid. The 1 Quart. Jour. Geol. Soc, vol. 28, 1872, p. Jenyns: Geol. Mag., London, 1866. (563) 90 DEPOSITS OF PHOSPHATE OF LIME. fBULL. 46. amount varies from 2 to 10 per cent, and is probably due to smallgrains of phosphatic matter iu Fig. 34. Distorted bed in Cambridgeshire, England; after O. Fislier: Geological Magazine, London>1871. A, shelly soil; B, clay or clayey gravel; C, white clay; D, phosphate nodule bed ; E, Gault. Phosphatic beds of Cretaceous Lower Greensand.—These beds occur be-tween the Coral Rag formation at the base and the Gault on the top>Their position with regard to these formations will be best seen in , section at Upware, The Coral Rag is a corallinerock varying much in texture, sometimes loose and porous, and at otherscompact and oolitic or arenaceous. Upon this the Kimmeridge Claysrest, probably But at some places, as at Upware, theKimmeridge Clay has been washed off the Coral Rag, which, in suchcases, often comes into direct contact with the overlying nodule , as a result of this destruction, there is a deposit of frag-ments o
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