ENCRINnES. 



119 



that we sometimes find nothing else? "Screw- 

 stones," the country folk call some of them — that 

 name being given in reality to those siliceous casts 

 of encrinital stems which occur abundantly in the 



Fig. gT.—Gly/>tocrmus (Silurian). 



Fig. 98. — Platycrhtus trl' 

 giniidactyhis (Carboni- 

 ferous limestone). 



Fig. 99. — Head of Actjnocriinis 

 cuspidatus (Carboniferous 

 limestone). 



chert-bands, where the original limy matter of the 

 ossicles (or individual joints of the stems) has been 

 dissolved away, leaving only thin plates of flinty 



