54 VIEWS OP THE MICROSCOPIC WORLD. 



In Sweden and Lapland, a white, mealy earth is found distributed in layers, 

 sometimes thirty feet in thickness. It is wholly composed of the shells of Diato- 

 macese, and when mixed with the ground bark of trees is used by the inhabitants 

 as an article of food in times of scarcity. The same kind of earth occurs in San 

 Fiora in Tuscany, and also near Egra in Bohemia, about three feet below the 

 surface of the ground. To the eye it appears when dry like pure magnesia ; but 

 when examined by the microscope, it is seen to consist entirely of a richly figured 

 species of a Diatom, which is called the Campilodiscus. A specimen from this 

 Fig. 81. locality, very highly magnified, is delineated in figure 81. Its 

 natural size varies from one-four hundred and thirtieth to one-two 

 hundred and fortieth of an inch. In the province of Luneberg, in 

 Saxony, a layer of this kind of earth also occurs, twenty-eight feet in 

 thickness, which is the greatest deposit that has yet been discovered: 

 and similar strata have been found in Africa, Asia, and the South 

 Sea Islands. On the banks of the Amazon, in South America, a bed of fine clay 

 occurs of the same nature. It is not a recent deposit from the swelling of the 

 river ; but is an ancient bed whose age is undetermined, and exists as an elevated 

 and extensive plain, shaded with woods and the thick foliage of forests. 



MICROSCOPIC FOSSILS IN CHALK AND FLINT. Chalk consists in a great measure of 

 fossil structures, together with minute shells, so exceedingly small that a million 

 distinct structures are computed by Ehrenberg to be contained in the space of a 

 cubic inch. These organic remains constitute nearly half the bulk of the chalk of 

 Northern Europe, and exceed this proportion in that of Southern Europe. The 

 portion of these chalk formations that is not organized was originally shells, which 

 having become decomposed, now form a cement for the organic remains, uniting 

 them together in one compact mass. The larger shells are perceived, when the 

 sediment obtained by brushing chalk into water is closely examined ; but in order to 

 detect the true microscopic structures, the following process must be adopted, which 

 has been pursued by Ehrenberg. A drop of water is first placed upon a thin slip of 

 glass, and then upon the water as much scraped chalk must be spread as will cover the 

 fine point of a knife. After leaving the chalk to rest for a few seconds, the finest 

 particles suspended in the water must be withdrawn, together with most of the 

 liquid, and the remainder suffered to become perfectly dry. This sediment must 

 now be covered with Canadian balsam, and the glass held over a spirit lamp until 

 the balsam becomes slightly fluid without froth or air bubbles. In this state it is 

 kept for a short time, until the balsam thoroughly penetrates every part of the 

 sediment, flowing into the chambers and cavities of the microscopic shells, and 

 causing their structure to be more readily detected. When a preparation thus made 

 is magnified three hundred times the chalk is seen teeming with minute organic 

 forms, the peculiarities of which are so clearly revealed, that the observer is enabled 

 to arrange and classify them with the utmost ease. Flint, to a large extent, has 

 also been proved to be of animal origin ; and a distinguished English naturalist has 

 observed, that masses of flint, or nodules as they are termed, are almost entirely 

 composed of the shells of minute animals, mingled with the scales of fishes, 



