38 LECTURE II. 



these animalcules, united togethex' without any visible cement ; in the 

 u^Dper and more compact masses the infusory shells are cemented 

 together, and filled by amorphous silicious matter, formed out of dis- 

 solved cases. Corresponding deposits of the silicious cases of these 

 animalcules have since been discovered in many other parts of the world, 

 some including fresh water species, others marine species of Infusoria. 

 At Egea, in Bohemia, there is a stratum of two miles length, and 

 averaging twenty-eight feet in thickness, of which the uppermost ten 

 feet are composed wholly of Infusoi'ia, including the beautiful shells 

 of Campylodiscus : the remaining eighteen feet consist of the silicious 

 cases of Infusoria mixed with a substance like pollen. The town of 

 Richmond, in Virginia, is built on barren silicious strata, twenty feet 

 in thickness, composed chiefly of Infusorial shells, including the well- 

 marked Actinocyclus and Coscinodiscus. A quantity of a pulverulent 

 matter is deposited upon the shores of the lake near Uranea in 

 Sweden, and which, from its extreme fineness, resembles floui*. This 

 has long been known to the poorer inhabitants under the name of 

 Berg mehl, or mountain meal, and is used by them mixed up with 

 flour as an article of food : it consists almost entirely of the silicious 

 shells of pulverised Polygastria, and of closely allied single-celled 

 locomotive plants. 



Most of the Infusorial formations, as the polishing slates of Cassel, 

 Planitz, and Bilin, are, in fact, extraordinary monuments, which have 

 handed down to us the record of the existence of polygastric Infu- 

 soria at remote periods of the history of this planet. Their minute 

 size, elementary structure, tenacity of life, and marvellous powers of 

 reproduction, have enabled them to survive, as species, those destroying 

 causes which have exterminated all the contemporaneous higher forms 

 of animals. Several species, for example, still exist, which were in 

 being at the period of the deposition of the chalk, and which contri- 

 buted their silicious remains to the flinty masses that are always 

 more or less intermixed with cretaceous matter. Existing species of 

 Polygastria have even been detected as low down as the Oolite. Be- 

 fore this discovery no remains of higher organised animals at present 

 in existence had been detected, with the same degree of certainty, 

 even in the cretaceous formation. A {qtn existing zoophytes and 

 testacea first make their appearance in the tertiary beds immediately 

 above the chalk ; hence called Eocene, from toe,, the dawn, as indi- 

 cating the first dawn of the creation of existing species. The num- 

 ber of existing species of shells increases in the ' Miocene,' and is still 

 greater in the ' Pliocene ' tertiary strata ; but the higher animals, as 

 the Anoplotheria, Palceothcria, Mastodons, Mammoths, and other 

 mammalian contemporaries of the Eocene, Miocene, or Pliocene tes- 



