60 



impregnation with silex, were simultaneous or took place at very 

 remote periods, can perhaps only be determined by future observa- 

 tions : the fact is however indisputable, the original matter, of which 

 the fabric of the animal was composed, has been removed, and its 

 place supplied by silicious matter deposited from its solution in some 

 appropriate menstruum. 



For the farther illustration of this interesting fossil, I have caused 

 various sections of it to be made, to admit of an examination of its parts 

 in different positions and directions. By a longitudinal section, much 

 of the real disposition of the plates composing the star is displayed, 

 the continued perpendicular plates may be distinctly traced, the ab- 

 sence of any transverse septa may be ascertained, and that plumose 

 appearance, which has sometimes procured for this fossil the appella- 

 tion of feather-stone, may be plainly seen. 



In Plate VIII. Fig. 39, of Bourguet's Traite des Petrifications, is a 

 very close representation of the characteristic forms which this fossil 

 assumes; although the figure is in other respects highly defective. 

 In the description of the plates, which is throughout lamentably 

 meagre, we only meet with champignon 6toil6 as the illustrative desig- 

 nation of the representation of this curious fossil. 



This fossil is exceedingly common in the northern parts of Wiltshire; 

 being turned up very frequently in the ploughed lands. 



Dr. Woodward evidently refers to this particular corallite under the 

 head of Coralloidea columnaria pentaedra; and specifies it as Coralloidea 

 oblonga pentaedra laminis a superfaie ad axem tendentibus. He de- 

 scribes a specimen, which he obtained from Wiltshire, as " A grey 

 semi-pellucid flint, the ground much like the Indian agate, but thick 

 set with white pentagonal columns, about a quarter of an inch in dia- 

 meter. They are made up of several longitudinal thin plates, all set edge- 

 ways towards the axis. The columns stand parallel to one another : 

 and are placed at equal distances, being about one-twentieth of an inch 



