FOSSIL SPONGES, ETC. 19 



will soon recognize, he may fill up some of these 

 numerous blanks in our information. The Portland 

 stone is in places crowded with tri-radiate sponge- 

 spicules ; the Kentish Rag is frequently so full of 

 the same objects that it hurts the hands of the men 

 who work in it. In the rocks of the Great Oolite 

 Mr. Etheridge says sponges abound, nine species 

 being known. 



At Haldon Hill, near Exeter, we have an outlier 

 of Greensand, where a thin layer contains lithistid 

 sponge-spicules very abundantly. Mr. Carter thinks 

 this bed of sponge-spicules may have been formed 

 along the sea-floor, after the manner in which a 

 similar layer of sponge detritus is now forming at 

 sea, about one hundred miles to the north of the Butt 

 of Lewis. 



The powder to be found in most hollow flints is 

 the best kind of material microscopically to examine 

 for spicules. Dr. Hinde, who has published an in- 

 teresting essay on " Fossil Sponge-Spicules from the 

 Upper Chalk," therein shows how much can be seen 

 and discovered by carefully examining only a few 

 ounces of this material. Those who have geologized 

 on the flints found in chalk strata are well aware 

 that the chalky material filling the hollow flints is 

 of a different appearance, both to the eye and the 

 touch, than the chalk itself. Dr. Hinde calls this 

 powder " flint-meal " a term which conveys a capital 

 idea of what it is like. Wherever there are chalk 



