Correspondence — Mr. J. Starkie Gardner. 479 



Fresh-water. Salt. 



Half a mile above Teddington Lock 66 



One mile below Teddington Lock 54 



Kew 52 37 



Blackwall 39 45 



Estuar}' of the Thames 9 60 



The examiuation of the hard diatom-rock of Nykjobing in Jutland 

 gave W. Prinz some interesting results as to the structure of some 

 Diatoms (see vol. i. p. 507). His views are criticized by A. Grunon, 

 p. 246, vol. ii. 



In the Tertiary shales of Warnsdorf, Bohemia, K. J. Taranek has 

 found remains of a Moss (Fo)itinalis ?), with Diatoms in a very good 

 state of preservation ; one of these [Melosira arenaria) still exists 

 in Bohemia. 



Mr. H. G. Hawks' enumeration of the uses to which diatomaceous 

 earth is applied (p. 785, vol. i.) is of great interest. It is used as a 

 material in the manufacture of soluble silica and soluble glass, of 

 porcelain, of some cements and artificial stones ; as manure ; as a 

 drying material in laboratories ; as a vehicle for mineral oil in light- 

 ing fires ; for making floating bricks ; in the manufacture of dyna- 

 mite, giant powder, lithofracteur, and other explosives ; and of 

 some soaps. It is said also to be an important constituent of at least 

 one tooth-powder (" sozodont ") ; and it has been used in packing 

 ice cases. 



That Sponge-spicules constitute the chief material of some chert 

 from the Carboniferous Limestone, as proved by Prof. W. J. Sollas, 

 is mentioned at p. 615, vol. i. 



A philosophic warning for geologists occurs in the abstract of T. 

 Fuchs's paper on Pelagic and Deep-sea Fauna, at p. 485, vol. ii., 

 where it is pointed out that aggregations of animals analogous to 

 those characteristic of abyssal depths may occur in the dark caverns 

 under the coral-reefs of Brazil, thus bringing deep-sea forms in near 

 contiguity with those of littoral habits. 



The very questionable occurrence of fossil organisms in meteorites, 

 supported by Hahn, Karsten, and Weinland, is noticed at p. 722, 

 vol. i. The refutation by Vogt is fully given at p. 176, vol. ii. ; and 

 has been already referred to in the Geol. Mag. Sept. 1882, p. 424. 



The notes on preparing thin sections of coal and mica-schist, at 

 pp. 577 and 578, vol. ii., are worthy of attention, T. R. J. 



COE-I^IBSIPOn^ZDIBl^CIE. 



ON THE CAUSES OF ELEVATION AND SUBSIDENCE. 

 Sir, — In June of last year I contributed an article to the Geolo- 

 gical Magazine in which I endeavoured to show that any addition 

 of weight on any part of the earth's surface produced a subsidence, 

 while anj'- removal of weight was followed by a tendency towards 

 elevation. The evidence I brought forward covering a very wide 

 range, and my article having been brief, I barely alluded to some 

 sections of it, and only remarked in reference to accumujations of ice 



