FOSSIL INFUSORIA. 61 



stone. It is highly remarkable from its being composed, to at least one-tenth of 

 its bulk, of Infusoria, and Prof. Ehrenberg has already recognised in it thirty 

 marine forms. This bed, which extends for five hundred miles along the coast, 

 and probably runs to a considerably greater distance, is more than eight hundred 

 feet in thickness at Port St. Julian." In volcanic products, which have been ne- 

 cessarily subjected to the action of the most intense heat, the remains of Infu- 

 soria have been detected, incredible as it may appear. The Island of Ascension 

 is of volcanic origin, and portions of a pink-colored, porous rock, which had once 

 been flowing lava, were here taken and preserved by Darwin. These speci- 

 mens were examined by Ehrenberg, who discovered, among other ingredients 

 of which they were composed, the flinty shells of fresh water infusoria. 



A large part of the sand of the great African desert, consists of the fossil 

 shells of animalcules ; and such is the fact in regard to the valley of the Nile. 

 Numerous specimens of the deposits of this river, taken from various localities 

 along its course from Nubia to the Delta, have been carefully examined by Eh- 

 renberg ; and in such profusion were fossil sponges, the flinty cases of Infusoria, 

 and various species of Polythalamia discovered, that not a particle of this soil of 

 the size of half a pin's head could be found, in which (allowance being made 

 for certain chemical changes that had occurred) there was not one, and often 

 several, of these fossil animals. 



MUD-BANKS. In the harbor of Wismar, on the Baltic, there is deposited, 

 every year, as appears from official documents, 228,854 cubic feet of mud ; and 

 the accumulation has continued at this rate for more than a hundred years. In 

 the course of a century a deposit has therefore been made to the extent of 

 22,885,400 cubic feet, equal to 3,240,000 hundredweight. These mud-banks 

 were examined by Ehrenberg in 1839 and 1840, and the surprising discovery 

 was then made, that from one-twentieth to one-fourth of the sediment was com- 

 posed partly of living Infusoria, and partly of the flinty shells of others that had 

 perished. On an average one-tenth part of the entire mass consists of micro- 

 scopic forms, and hence the annual deposit of animalcules in the port of Wismar 

 amounts in bulk to 22,885 cubic feet, which, if it was dried, would weigh 

 not far from forty tons. In the mud-banks of Pillau, Infusorial animalcules 

 were found in greater abundance than in those of Wismar. At both localities 

 many of the forms were entirely new, and others were identical with living In- 

 fusoria that inhabited the waters of the neighboring seas. 



The mud deposited by the Elbe at Cuxhaven, was found by Dr. Ehrenberg to 

 be extremely rich in animalcular remains nearly half of the sediment consisting 

 of the flinty cases of Infusoria, and various species of the Polythalamia or many- 

 chainbered shells. The flinty cases of Infusoria have been found at the bottom 

 of the ocean in the mud of the coral islands beneath the equator, and no less 

 than sixty-eight species have been discovered in the mud at Erebus Bay, near the 

 Antarctic pole. The examination of the sediment deposited along the Atlantic 

 coast of America, has revealed similar facts. Infusorial animalcules have been de- 



