Royal Microscopical Society. 69 



II. — Diatomaceous Earth from the Lake of Valencia, Caracas. 



By A. Ernst, Esq., and H. J. Slack, F.G-.S. 



{Bead before the Koyal Microscopical Society, June 7, 1871.) 



The following letter accompanied a present to the Society of dia- 

 tomaceous earth from the Lake of Valencia, Caracas : — 



To the Secretary of the Royal Microscopical Society, London. 



Cakacas (Venezuela), Dec. ith, 1870. 

 Sib, — Allow me to present to the Eoyal Microscopical Society the 

 included specimen of diatomaceous earth from the neighbourhood of 

 the Lake of Valencia in this country. This lake is known for the 

 progressive diminution of its waters, and was formerly very much 

 larger than it is at present. An interesting account of it is given by 

 Humboldt, 'Personal Narrative,' ii., 1-20 (Bohn's edition). All 

 round the lake, to a very considerable distance, extends a deposit 

 called by the inhabitants tierra de caracolillo, i. e. earth (formed) of 

 small shells, undoubtedly the old bottom of the lake. It forms a layer 

 of several feet of thickness, in which there are imbedded numberless 

 specimens of small shells. I have hitherto found six different species, 

 of which I add samples. Nos. 1-4 are very abundant ; 5 and 6 are 

 very rare. I hope one of your conchologists will have the kind- 

 ness to determine the species. The remainder of the layer has the 

 appearance of a greyish blue marl, and contains so great a number of 

 fossil diatomaccEe that it may be said to be entirely formed out of 

 them. Being myself not sufficiently acquainted with diatomaceaB, I 

 must leave the closer inspection of this earth to others, and I feel sure 

 that one of the members of the Koyal Microscopical Society will 

 kindly give us a list of the species it contains. 



I shall be very happy to send a sample of the tierra de caracolillo 

 to any microscopist or geologist who would like to have some. 



I have the honour to be, Sir, 



Your obedient servant, 



A. Ernst. 



Humboldt visited the Lake of Valencia about the beginning of 

 the present century. He describes the lake as then resembling 

 that of Geneva in appearance, and that of Neufchatel in size, and 

 makes many remarks on its progressive diminution, which he 

 ascribed to local changes, increasing evaporation, and diminishing 

 the water supplies. He remarked, " The land that surrounds the 

 Lake of Valencia being entirely flat and even, what I daily observed 

 in the lakes of Mexico takes place here ; a diminution of a few 

 inches in the level of the water exposes a vast extent of ground 

 covered with fertile mud and organic remains." * He advised the 



* 'Personal Narrative,' Helen Maria Williams' trans., vol. iv., p. 151. 



