Geology of the Eastern Desert of Egypt. 137 



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 deep 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 Forbes's 

 Asteropeeten Orion, from a sandstone bed of the Kellaways rock 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; the sand contained no 

 soluble material, like that which filled the chambers of the Nautilus. 

 But in the lowest beds of the Coralline Oolite at Filey Bri gg, 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 Nautilus also 

 filled the cavity left by the decay of the starfish 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. " Notes on the Geology of the Northern Etbai or Eastern 

 Desert of Egypt ; with an Account of the Emerald Mines." By 

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



The principal feature in the district is a long ridge of igneous 

 upthrust running N.N.W. and S.S.E., in which porphyry rises into 

 lofty peaks, whilst the lower parts are formed of granites and sedi- 

 mentary rocks. To the west of the watershed, sedimentary rocks 

 occur dipping slightly to the west. 



The following succession of rocks in descending order is given by 

 the author : — Limestone, sandstone, clay, * cataract '-rock (cor- 

 responding to the SfocJc-f/ranit of Walther), and compact hard 

 granite. The sedimentary rocks are frequently metamorphosed, and 

 the author states that every stage of metamorphism is shown, from 

 sandstone to compact green granite. The blue clay shows various 

 kinds of metamoxphism, and forms the pistachio- breccia containing 

 topazes, and the mica- schist, mica-slate, and talcose blue clay of the 

 mass of Zabbara containing emeralds. 



The author discusses certain theoretical questions, and considers 

 that the erosion of the valleys does not indicate the existence of a 

 greater rainfall than the present one. He concludes by giving an 

 account of the emerald mines. 



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

 Esq.,B.Sc. 



In this paper attention is called to certain recorded discrepancies 



