1872.] S0LLA8 TJPPER-GREENSAND COPKOLITES. 77 



between calcic phosphate and animal matter in the case of the 

 " Coprolites." 



The Blackdown silicified shells were next explained ; and it was 

 reasoned that the state of their silica offered arguments tending to 

 prove a passage of silica from the colloidal to the crystalline state. 



Part II. 



Coprolites, as has already been stated, are the result of the 

 phosphatization of organic matter. They may be classed according 

 as their origin is known or obscure. The progress of discovery 

 transfers the obscure forms into the class of known forms ; but there 

 will always remain a certain number which cannot be thus trans- 

 ferred—those, for instance, which have been produced from soft- 

 bodied animals in the last stage of decomposition, all traces of their 

 structure having been obliterated. The fossil remains of Reptiles, 

 Fish, and Crustacea, the casts of Mollusks, and the perfectly pre- 

 served Ventriculites are instances of coprolites about whose origin 

 there is no uncertainty ; but besides these easily recognizable kinds 

 there remain a vast majority of forms which, from their want of 

 any striking characters, have always been obscure. In this paper 

 the author proposes to transfer these in great part among the fossil 

 sponges. 



General Character of the Coprolites. 



In the Greensand, most of the coprolites are of a black or deep 

 brown colour, while in the Gault they are greyish-white on the 

 surface, but brownish-black internally. By etching the greensand 

 coprolites with acid they change, however, to the same greyish- 

 white colour as the specimens from the gault ; and masses of 

 agglomerated coprolites are met with in the Greensand which, when 

 broken open, reveal nodules of their original light colour. 



The surfaces of most of the coprolites are variously marked with 

 (i.) fold-like depressions, (ii.) osculiform pits, (iii.) puncta, and (iv.) 

 contraction cracks. 



(i.) The depressions occur as fold-like markings, which some- 

 times run longitudinally with remarkable constancy in size and 

 direction for nearly the whole length of the fossil; besides this 

 they may take any other direction. These grooves are marked 

 by very minute wrinkles, which give the whole depression the 

 appearance of one of the creases stretching from button to button in 

 the leathern back of an easy chair. The better-marked of these 

 grooves scarcely appear to be due to contraction consequent on 

 fossilization. 



(ii.) The circular or oval osculiform pits vary in size, frequently 

 being -^ of an inch in diameter. Their margins are often de- 

 pressed into a concave border, which is striated by regularly ra- 

 diating " groovelets." These commence at the sides of the osculi- 

 form pit, pass across the concave border, and either stop there or 

 pass to a greater or less distance on the surrounding surface. In 

 some specimens these little striations are more restricted and better- 

 defined than in others, and in some they are altogether absent. 



