PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 1 85 



chamber is filled with foraminiferal ooze, the component objects 

 of which are almost as perfect as when the organisms were living. 

 The surrounding limestone is chiefly in an amorphous state ; but it 

 contains innumerable evidences that it also consists of foraminiferal 

 ooze, largely reduced to the amorphous state by the agency of car- 

 bonic acid, now known to be so abundant in the depths of the 

 ocean. The action of this acid upon the minute calcareous shells 

 necessarily converted the water into a solution of carbonate of 

 lime. In this state it percolated by osmosis through the shell of 

 the Kautilus, penetrating its closed chambers, which it gradually 

 filled with calcareous spar. The specimen is thus an epitome, 

 within its limited area, of what has taken place on a gigantic scale 

 in the deej) sea. We have here first the organic mass, next its 

 conversion into amorphous limestone, and lastly the production of 

 the crystalline state of the same, so frequently seen filling the 

 interiors of fossils. 



The second object is the original type-specimen of Porbes's 

 Asteropecten Orion^ from a sandstone bed of the KeUaways Eock in 

 the neighbourhood of Pickering, in Yorkshire. This starfish had 

 lived upon and became buried in a sandy matrix which contained 

 no lime. When the rock was split open, the space originally 

 occupied by the starfish was hollow ; for the sand contained no 

 soluble material, like that which filled the chambers of the jN'autilus. 

 But in the lowest beds of the Coralline Oolite at Filey Brigg, on the 

 Yorkshire coast, we long ago found another species of starfish, 

 closely allied to the Pickering species. This was embedded in cal- 

 careous stone, which had once in all probability been foraminiferal 

 ooze, and the processes which filled the chambers of the NautHus also 

 filled the cavity left by the decay of the starfi:sh with crystalline 

 carbonate of lime. 



These specimens, studied collectively, illustrate two of the most 

 important and common of the processes by which the mineralization 

 of fossil remains has been effected. 



The following communications were read : — 



1. " jS^otes on the Geolog}^ of the iJforthern Etbai or Eastern 

 Desert of Eg^^pt ; with an Account of the Emerald Mines." By 

 Ernest A. Floyer, Esq., F.L.S., F.G.S. 



2. " The Eise and Fall of Lake Tanganyika." By Alex. Carson, 

 Esq., B.Sc. (Communicated by E. Kidston, Esq., F.E.S.E., F.G.S.) 



May 11th, 1892, 

 W. H. Htjdleston, Esq., M.A., F.E.S., President, in the Chair. 

 The list of Donations to the Library was read. 



