THE 'DERIVED' FOSSILS. 31 



the shell itself is left upon the exterior, and only faint traces of the 

 ribs of the inside cast remain. The umbilicus is filled with an 

 irregular mass and protuberant lumps of phosphate of lime, often 

 exhibiting fragments and impressions of other fossils. No abrupt 

 shell-apertuie now breaks the contour of the body, all this having 

 been worn down flush with the general outline. Thus the action 

 of the waves has changed the beautiful Ammonites biplex into an 

 unsightly mass; and the work of mutilation has been further 

 carried on by crowds of worms, sponges (?), Lithodomi, vlrca-like 

 shells, Pholadidea and such rock-boring animals, whose empty 

 crypts now stud the surface of the relict of the Ammonite and its 

 adherent phosphate. But within this mass the inner shell-whorls 

 have been protected and saved from destruction by the older enfold- 

 ing coils; and often, under a stroke of the hammer the central part 

 will jump out in all its original freshness, a brilliant new birth 

 glistening, it may be, with a charming play of iridescent colours 

 from its pearly shell layer. 



The ether example is a bivalve shell of the Anatinidce, com- 

 monly referred to Myacites. Here the shell is totally lost, and the 

 original outline of the interior phosphatic mould has been to a 

 great extent destroyed by wave-action, the umbo, pallial border, 

 and all the margin being completely denuded into rounded outlines. 



The Upware phosphates are smaller and very much more 

 worn than those of Bedfordshire. 



The derived fossils belong to various ages, ranging at least 

 from the Neocomian to the Oxford clay inclusive. 



I. The 'Derived' Neocomian Fossils. 



A. The Phosphatised Forms. 



One of the most surprising facts connected with our Upware 

 deposit is the occurrence of undoubted Neocomian species as de- 

 rived fossils. Ammonites Deshayesii and two species of Ancylo- 

 ceras occur at Upware in as thoroughly phosphatised and battered 

 conditions as the Ammonites biplex and other species of the inferior 

 Jurassic rocks. In both cases the shells have been fossilized in their 

 original sediments and washed out of the old sea cliff or sea bed, 

 just as fossils are now washed out and scattered along the beaches 



