70 Transactions of the 



rich landholders to place columns of granite in the basin of the lake, 

 and note the mean height of the waters from year to year. At the 

 time of his visit the mean depth of the lake was from twelve to 

 fifteen fathoms, and in the deepest parts thirty-five or forty feet. 

 He said, "It is impossible to anticipate the limits, more or less 

 narrow, to which this basin of water will one day be confined, when 

 an equilibrium between the streams flowing in and the produce of 

 evaporation and filtration shall be completely established. The idea, 

 very generally spread, that the lake will soon entirely disappear, 

 seems to me chimerical. If in consequence of great earthquakes, 

 or some other causes equally mysterious, ten very humid years 

 should succeed to long drought; if the mountains should clothe 

 themselves anew with forests, and great trees overshadow the shore 

 and plains of Aragua, we should probably see the volume of the 

 waters augment and menace the beautiful cultivation which now 

 branches on the basin of the lake," 



The diatomaceous deposit of which Mr. Ernst has sent a speci- 

 men is remarkably rich in quantity of specimens ; and it will interest 

 microscopists to note some of the conditions, described in the pre- 

 ceding quotations, under which it has taken place, 



A shallow lake, fed by numerous small rivers, having no sea 

 outlet, and a warm temperature such as that of Valencia, seems 

 very favourable to diatom life, and the preservation of the shells. 

 Humboldt thought much of the water in the interior of Australia 

 was in a similar condition ; and friends of science who may have 

 opportunities of visiting such localities will do well to follow Mr. 

 Ernst's example, and forward specimens to the Society. 



The fresh-water shells sent by Mr. Ernst have been named by 

 Mr. Henry Woodward, and consist of the following species, the 

 numbers being those on the little bottles containing them: — 

 l.Plauorbis; 2. Paludina (pygmsea?),; 3. Bithynia; 4. Melania; 

 5. Physa ; 6. Ancylus. 



The diatoms, so far as they have been examined, do not seem to 

 present any unusual forms. They will be still further investigated 

 by Fellows of the Society who devote attention to this particular 

 subject. 



