FOSSIL INFUSORIA. 59 



wjht hundred feet in thickness at Port St. Julian." In volcanic products, which have 

 been necessarily subjected to the action of the most intense heat, the remains of 

 protophy tes have been detected, incredible as it may appear. The Island of Ascen- 

 sion 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 protophytes. 



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

 of small animals ; and such is the fact in regard to the valley of the Nile. Numer- 

 ous specimens of the deposits of this river, taken from various localities along its 

 course from Nubia to the Delta, have been carefully examined by Ehrenberg ; and 

 in such profusion were fossil sponges, the flinty cases of Diatoms, and various spe- 

 cies 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 

 organisms. 



MTJD-BANXS. 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 accu- 

 mulation 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 hundred weight. These mud-banks were examined by Eh- 

 renberg in 1839 and 1840, and the surprising discovery was then made, that from 

 one-twentieth to one-fourth of the sediment was composed partly of living Diatoms, 

 and partly of the flinty shells of others that had perished. On an average one-tenth 

 part of the entire mass consists of microscopic forms, and hence the annual deposit 

 of these structures 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, the remains of Diatoms 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 protophytes 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 organic remains nearly half of the sediment consisting of the 

 tlinty cases of Diatoms, and various species of the Polythalamia or many-chambered 

 shells. The flinty cases of protophy tes 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 spe- 

 cies have been discovered in the mud at Erebus Bay, near the Antartic pole. The 

 examination of the sediment deposited along the Atlantic coast of America, has 

 revealed similar facts. Diatomaceous forms have been detected in the mud of Bos- 

 ton harbor, and in the marine marshes at New Haven in Connecticut; and numer- 

 ous elegant infusorial structures and many- chambered shells have been found at 

 Amboy in New Jersey, in the mud adhering to oysters as they were taken from 

 their beds. 



In view of facts like these, it has been asserted by naturalists, that the deposits 



