208 Dr. W. B. Clarke on the Crag of Suffolk. 



B. Longitudinal view of the same fossil, half the natural size. 



All these fossils are in a highly mineralized state, apparently- 

 produced by the ferruginous particles contained within the Crag, 

 in conjunction with certain peculiar conditions of the fossil 

 itself. 



With the above are also found teeth and vertebras of several 

 species of fish allied to Sharks, some extremely large, as the Car- 

 charodon megalodon : the spines, tubercles, and teeth of Rays, 

 some of which are completely mineralized, and others not, but 

 partaking of the condition of the generality of fossils of the Crag 

 epoch : amongst these are found specimens of fish derived from 

 the London clay, surrounded more or less by their argillaceous 

 matrix. In the same condition are found short- and long-tailed 

 (Brachyurous and Macrurous) crustaceans all highly mineralized, 

 the greatest amount of which occur beneath the general Crag- 

 deposit ; but in various parts throughout the Bed Crag formation 

 are found the claws of Crabs in the usual condition of the Crag 

 fossils, without any appearance of mineralization, but in an ex- 

 tremely friable state from their having lost their animal matter : 

 with these are associated spines of Echini and flints from the 

 Chalk. 



As the mammalian remains contain a large proportion of 

 phosphate of lime, considerable interest has been attached to 

 them of late : the Crag has been laid open, carefully overlooked, 

 and these remains collected and preserved for agricultural pur- 

 poses after having been ground to powder and converted into 

 superphosphates by digestion in sulphuric acid. The argilla- 

 ceous nodules when thus ground are said to be used in large 

 quantities in the adulteration of guano and bone-dust, and thus 

 applied by the agriculturist. 



At intervals are found beds of ferruginous clay nodules, which 

 upon being broken present a highly mineralized crust or exte- 

 rior, containing a pulverulent ochreous substance; these are 

 usually of a flattened form, and lie parallel with the plane of 

 stratification. The mineralization of these nodules probably con- 

 tinues to the present time through the agency of ferruginous 

 matter involved in the Crag. 



