VIEWS OP THE MICROSCOPIC WORLD. 



in harbors, and the accumulation and amazing fertility of the mud of the Kile, and 

 probably of other turbid rivers, are to be attributed in a great measure to the agency 

 of invisible forms, whose countless generations succeed each other with astonishing 

 noidity, leaving the curious structures in which thev were encased as the durable 

 rt ;ords of their existence. 



These gradual accretions have loeen accumulating for centuries, and are at this 

 moment still in progress. The sea now swarms with races of minute organisms, 

 whose fossil types are continually discovered in beds and strata of unknown anti- 

 quity. In salt water, taken from Cuxhaven and various other places, no less than 

 twenty genera and forty living species have been discovered by Ehrenberg, which he 

 regards as identical with those occurring in the chalk formations. And out of twenty- 

 eight species of fossil structures belonging to the various species of the Diatoraaceae, 

 he has detected fourteen fresh water and five marine species, now living; the 

 remaining nine are either unknown or extinct forms. 



The Diatomaceae that crowd the seas are devoured in multitudes by the common 

 scallop and other molluscous animals; for when their stomachs are examined they 

 are found to contain thousands of microscopic flinty shells, which, from their nature, 

 were incapable of being digested. When a few atoms of the food which a scallop 

 has taken into its stomach is viewed by the microscope, it is found teeming with a 

 rich collection of curious shells, closely resembling the beautiful structures that con- 

 stitute the Richmond deposit, not only in form but in arrangement so striking is 

 this resemblance, that it is said to be extremely difficult to distinguish between the 

 recent and ancient remains ; and that even an experienced observer would be 

 liable to confound them, unless the glass slides, upon which they were mounted, 

 were labeled. 



The guano imported from the isle of Ichaboe has been found to contain the beau- 

 tiful shell of the Coscinodiscus, and other Diatomaceous structures of great elegance 

 and richness ; and, as we gaze upon these minute cases, we cannot fail of being 

 struck with the fact of the great resistance to decomposition which they possess. 

 In this instance they must have gone through the process of digestion twice, and 

 been subjected to the action of the elements for centuries. Guano, as is well known, 

 is found within certain latitudes on uninhabited islands, which have been, for ages, 

 the abode of innumerable multitudes of marine-birds. It consists of their excre- 

 ments, which have been accumulating for century after century, until they form 

 layers of great thickness ; many beds having been discovered in the islands of the 

 Pacific, off the Peruvian coast, having a depth of thirty-five or forty feet. The 

 siliceous shells, detected in the guano, are the remains of Diatoms devoured by fish, 

 which, afterwards, became the prey of voracious sea-birds. Thus the shell passed 

 through the stomach twice, and then remained in the guano-bed for an unknown 

 length of time, subjected to those common causes of decay which turn the solid 

 rock itself to dust. But under all these influences they continue unchanged, and 

 the eye of the naturalist at last detects these minute structures still possessing their 

 original beauty, with the delicate tracery of their rich configurations, almost as 

 sharp and clear as it was, perhaps, a thousand years ago. 



