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deposits, averaging each about a foot in thickness. The beds 
are less ferruginous, and contain more lime than those in 
Bedfordshire. They afford many fossils, some of which are 
derivative, and others lived in the sea in which these 
deposits were formed. Mr. Walker, of Cambridge, who 
first drew attention to these sections, in some valuable 
Papers published in the Annals of Natural History, 1866 
and 1867, believes them to be of the same age as the con- 
glomerate bed, near Potton and the Farringdon Sands, and 
therefore belong not to the upper but lower Green Sand. 
In the Green Sand at Farnham, in Surrey, nodules chiefly 
composed of calcic phosphate, are found in abundance, and 
have been extensively employed for economical purposes. 
Similar concretions are also present in the Gault, a stratum 
of blue clay, which intervenes between the upper and lower 
Green Sand. The chalk marl where it immediately overlies 
the upper Green Sand also contains them. True coprolites 
occur in the chalk, but are too widely diffused to be of any 
commercial value. In the Lias, large coprolites of Saurians 
are met with, especially at Lyme, and these might possibly 
be collected and made available as a manure. These may, 
perhaps, be sought for when the Crag and Green Sand 
phosphate beds are exhausted, as they must be in time. At 
present it is these two formations which yield the greatest 
part of our Geological Phosphates. It is perhaps well to 
note that the Phosphate Beds in the Crag and Lower Green 
Sand present these points of identity, that they are probably 
extraneous, derived from other and older formations, and 
that a large proportion of the fossils are the same and much 
water-worn. We now come to the interesting question from 
what source these concretions derived their phosphatic 
matter. Although Calcium phosphate is known as a simple 
