THE REVOLUTIONS OF THE CRUST OF THE EARTH. 317 



seven of which belong to the family of the palms. The Cycads formerly 

 so important, accompany the conifers, starting with the Coal forma- 

 tion, and attaining their maximum of development in the Keuper and in 

 the Freestone, and diminishing in importance in the Chalk. The princi- 

 pal gonera of this family are Cycadites, Zamites, Ptcropliyllum, Nilsonia. 



The conifers, formerly always accompanied with palms, are now 

 found from the warm regions of the equator to the inhospitable glacial 

 zone. Their genera, Pinitcs, Abietites, Araitcaria, Toltzia, Junipcritcs, 

 Cupressites, Thuites, Taxites, and others, are still extensively distributed, 

 and do not appear to have lost vitality. 



The Dy cotyledons, of which only a few traces are found in the last 

 strata of the Secondary period, appear suddenly in the Tertiary period, 

 and predominate in almost all the continents. These plants, with their 

 large leaves, beautiful flowers, and succulent fruits, change entirely the 

 aspect of the flora, while under the shadow of their great branches and 

 in their thick foliage animal and vegetable life find shelter and protec- 

 tion. 



In the animal as in the vegetable kingdom there is progressive im- 

 provement in the organization of the living creatures which have suc- 

 cessively inhabited the terrestrial globe ; but in general the importance 

 of their fossil remains is inversely proportional to the development of 

 this organization. Thus the Infusoria* have left great beds, siliceous or 

 cretaceous, almost eutirely composed of their shells; and, in our day, 

 in many parts of North Germany there are vast extents of country 

 where, at a few yards from the surface, the damp soil is principally 

 composed of living Infusoria. The city of Berlin is built upon such a 

 soil. The Polythalamia and the Foraminifcra, generally very small, are 

 particularly abundant in the Chalk, which is almost entirely composed 

 of them. The JS'ummulites, cemented by a clayish substance, form enor- 

 mous deposits in the Upper Chalk. 



The Polyps appear with the first sedimentary deposits of the transi- 

 tion period, but their principal genera quickly disappeared. Thus the gen- 

 era Catenipora, Syringipora, hardly reached into the Carboniferous lime- 

 stone. From that time until the Jurassic formation the genera Gorgonia 

 and CythophjUum prevailed. During this formation appeared the genera 

 Scyphia, Tragos, AcJiiUum, Manon, and Astrca, which are recent, while the 

 Cuemidies rapidly disappeared. Until the Chalk period we find prin- 

 cipally the Syphonia; the Ventriculites and the Hippurites, which are 

 classed to-day, in spite of the authority of von Bach, with the bivalve 

 mollusks belonging exclusively to the Chalk. 



The Crinoids, under very elegant forms, are very numerous before the 

 Chalk, but during the formation of the Cretaceous strata they disappear 



"Many strata of microscopic fossils must bo attributed, according to certain micro- 

 graphs, not to the Infusoria, but rather to the Diatomaca and to the Desmidia, the sili- 

 ceous carapaces of which were regarded by Ehrenberg as the remains of microscopic 

 animals. 



