190 SUPPLEJIENTARY NOTES. 



that have since elapsed have been fruitful in results of the most important and interesting 

 character ; from every quarter of the world, from the loftiest mountain peaks, and from the 

 deepest recesses of the ocean which the plummet can reach, from the ashes of volcanoes and 

 from the snow of the glaciers, the durable remains of Infusoria have been obtained. That 

 excellent scientific periodical, Silliman's American Journal, contains numerous interesting 

 communications on this subject from the eminent chemical professor of the Military College 

 at West Point, Dr. J. W. Bailey ; and the labours of Mr. Bowerbank, WilHamson, and other 

 active members of the Microscopical Society of London, have yielded much interesting infor- 

 mation on the infusorial deposits of our own country. 



The present note will be restricted to remarks on the nature of the organisms which enter 

 so largely into the composition of certain tertiary deposits ; since the opinion once entertained 

 of the animal nature of many infusoria, now regarded as true vegetables, materially affects the 

 geological conclusions respecting the persistence of certain species of organisms through long 

 periods of time, during which the moUusca, zoophytes, &c. underwent repeated mutations both 

 in the species and genera. Thus, for example, the polierschiefer, or polishing-slate of Bilin, 

 and the berghmehl of Tuscany, are described by Ehrenberg as masses of the siliceous shells 

 of animalcules of such extreme minuteness, that a cubic inch of the stone contains upwards of 

 forty millions ; the infusorial earth of Richmond, in Virginia, in like manner, is stated to be 

 made up of the siliceous skeletons of animalcules of infinitesimal minuteness. But later inves- 

 tigations have (I conceive) satisfactorily established, that the greater part of these fossil organisms 

 belongs to the vegetable and not to the animal kingdom.' The whole of the figures in Plate IV. 

 of the " Medals of Creation,'' described as living Infusoria, on the authority of Ehrenberg, are 

 undoubted vegetables, belonging to the great botanical groups called Diatomacece (from the 

 angular segments into which they separate by partial division), and DesmidiaceteJ The entire 

 family of Bacillaria belongs to this group. These simplest forms of vegetable structures abound 

 in every lake or stream of fresh and brackish water, in every pool, or bay, and throughout the 

 ocean, from the equator to the poles ; they secrete siliceous envelopes, which present an endless 

 variety of form and structure, and after the death and decomposition of the perishable tissues 

 of the plants, remain as perfectly transparent colourless shields of pure silica ; such are the 

 Gaillonelloe, Euastra, Closteria, Namculce, SynhedrcB, Podosphenice, Xaniliidia, &c., which constitute 

 so large a proportion of the infusorial earths described by Ehrenberg and other authors.^ 



The extent of this infinitesimal fiora throughout regions where no other forms of vegetation 

 are known, is strikingly demonstrated by the observations of the eminent botanist and traveller. 

 Dr. Hooker, in his account of the Antarctic regions. 



" Everywhere," he states, " the waters and the ice ahke abound in these microscopic vege- 

 tables. Though too small to be visible to the unassisted eye, their aggregated masses stained the 

 iceberg and pack-ice wherever they were washed by the sea, and imparted a pale ochi-eous 

 colour to the ice. From the south of the belt of ice which encircles the globe, to the highest 

 latitudes reached by man, this vegetation is everywhere conspicuous, from the contrast between 

 its colour and that of the white snow and ice in which it is imbedded. In the eightieth degree 



' In my little work on Eecent Infusoria, entitled " Thoughts on Animalcules, or a Glimpse of the Invisible World 

 revealed by the Microscope," I have expressed my conviction of the vegetable nature of these organisms, as a reason for 

 omitting iigures and descriptions of any of the species in a work on living fresh-water animalcules. 



2 The name Diatomaceee is restricted by M. Brebisson to those species which have a siliceous envelope, or cuticle ; and that 

 of Desmidiss to those which are not siliceous, but reducible by heat to carbon. 



' The reader interested in this subject should consult the beautiful work of Mr. Haasall on the Desmidiaceas, published 

 by Messrs. Beeve & Benham. 



