32 THE UNIVKRSE. 



they have now and then produced a perfect fossilized ani- 

 mal meal. Nothing more is required than to make it into 

 bread. In fact, it is well known that in times of dearth 

 the Laplanders nourish themselves with a white mineral 

 dust, which they substitute for cereal products. Retzius, 

 who examined this meal, found that it is composed of nine- 

 teen species of Infusoria, analogous to those which now 

 live in the neighborhood of Berlin ; and the learned pro- 

 fessor has even shown that this skeleton dust, which is 

 spread equally through Finland and Sweden, owes its nutri- 

 tive qualities to a certain amount of animal substance, which 

 chemical analysis detected after so many, many ages ! 



Thus modern science throws her vivid light upon a crowd 

 of facts which till our day remained hidden in darkness. 



CHAPTER IV. 



CITIES BUILT OF MICROSCOPIC SHELLS. 



IN following our studies progressively, if we pass from 

 organisms so small as absolutely to escape the eye to those 

 the shell of which approaches a pin's head in size, we see 



on-loads consumed. Many of these deposits are especially interesting on this 

 account, that their upper beds consist of diatoms that are still living. To this 

 class belong the deposit not far from Ebsdorf, in the Luneburg Heath, which is 

 about thirty feet in thickness, and, according to Ehrenberg, is composed of some 

 thirty different species of diatoms. The prevailing species is, however, Synedra 

 acuta, whose hard coverings appear in the form of long ladder-like bodies. Next 

 to it the most conspicuous are Pinnularia incequalis (the crooked, ship-formed 

 bodies, marked with cross-lines), and Gallionella varians (the large round discs). 

 Willkomm, Die Wunder des Mikroskops. 



