REV. F. WOLLE'S OPINIONS 107 



the contents of the cells and the whole tissue 

 of the plants have gone except the siliceous 

 coats. The mass is from a fresh-water lake 

 in Australia. Year after year the diatoms 

 in myriads lived for a short time in the 

 water; when dead, the organic portions 

 decayed, and the remaining imperishable 

 siliceous coats fell to the bottom of the lake, 

 and in time formed the pure deposit of 

 which this is a fragment. 



' As regards the longevity of diatoms/ 

 says the Kev. F. Wolle (Diatomacece of North 

 America), l it may be said that dried speci- 

 mens cannot be revived, but they have been 

 known to survive nearly a quarter of a 

 century in their natural element, even though 

 kept for long periods in the dark, and at 

 times frozen in solid ice. Their siliceous 

 covering is almost indestructible, resisting the 

 strongest acids and passing unscathed through 

 very high degrees of heat.' 



Specimens for mounting can readily be 

 collected in a wide-mouth bottle, with some 

 fine muslin to act as a net. When the 



