306 Seeley — Rock of the Cambridge Greensand. 



An analysis by Dr. Augustus Voelker, F.C.S., gives : — 



Moisture and organic matter 4-68 



Lime , 43-21 



Magnesia 1'12 



Oxide of iron 2-46 



Alumina 1*36 



Phosphoric acid 25-29 



Carbonic acid 6-66 



Sulphuric acid 0-76 



Chloride of sodium 0*09 



Potash 0-32 



Soda 0-50 



Insoluble silicious matter 8-64 



Fluorine and loss 4*96 



100-05 



Now, as many of the concretions are rolled, there must have been 

 gelatinous phosphate of lime on the shore. Sea-weeds contain 

 in their ashes about 2 per cent, of phosphoric acid, these growing 

 on a shore where no sediment was brought, must, during a whole 

 geological period, have accumulated and set free by decomposition a 

 prodigious quantity of phosphoric acid. An additional quantity would 

 have been furnished from decaying animals, which, combining with 

 lime, would be in a gelatinous state, and insoluble in water ; this has 

 been rolled into nodules with carbonate of lime and materials on the 

 strand. The phosphatic nodules of the Crag appear to have had a 

 similar and concretionary origin. But it is not impossible that denu- 

 dation of deposits in the Palaeozoic Eocks, as of Estramadura, may 

 have assisted in furnishing the material for the nodules of phosphate 

 •>Qf lime which abound in all our Cretaceous rocks. 



And now of the components of the rock there only remain to be 

 noticed the chalky mud, consisting chiefly of Foraminifera, similar to 

 those of the Chalk, and the other fossils. 



These scattered through the bed are all badly preserved. Bones 

 are mineralized with phosphate of lime, almost invariably broken, 

 and rarely occiu' in a series referable to one animal ; and when this 

 does happen the associated bones are generally washed into pockets of 

 the Gault. They include birds, saurornia, two ichthyosaurs, numerous 

 plesiosams, polyptychodon, if such a genus exist, several genera of 

 chelonia, crocodiles, lizards, dinosaurs, and numerous sharks, chime- 

 roids, and bony-scaled and soft-scaled fishes. Some of the reptiles are 

 certainly land animals, others are as unquestionably marine, though 

 nearly all could travel on the shore.^ 



The mollusca are all well represented, but there are no examples 

 that can be considered as land shells. Nearly all the shells having been 

 formed of arragonite are recognised only by their moulds in phosphate 



1 Notes on some some of the Mollusca and Echinoderras of the Upper Greensand 

 will be found in the Annals of Natural History for February, April, and July, 1861, 

 and October, 1865. And on the Pterodactyles, for February,' 1865, and May. 1866. 



