FOSSIL KELICS. 125 



there their remains accumulate layer upon layer, forming 

 beds of" vast thickness, which at a future day may be laid 

 bare, covered with alluvium, and engage the researches of 

 another Cuvier. The chemical action of the atmosphere ; 

 heat and cold, rain and snow, winds, springs, rivers, 

 torrents, the action of the tides ; life, animal and vege- 

 table ; and volcanic agencies, all contribute their part to 

 alter the surface of the land, and to effect changes in its 

 relative extent to that of the sea — changes which are in 

 reality never stationary, but, imperceptible as they may 

 seem, in constant progress. 



The deposits of the Tertiary period are divided by Mr. 

 Lyell into three series : the oldest, or Eocene, in which 

 there occurs from three to five per cent, of existing spe- 

 cies of shells ; secondly, the series of the middle age, or 

 Meiocene, averaging 18 per cent, in the occurrence of 

 existing species of shells ; and thirdly, the superficial or 

 Pleiocene deposits, in which the ratio of existing shells is 

 from 40 to 95 per cent. 



We trust we shall be pardoned for this brief digres- 

 sion, into which we were led by a desire to show that 

 fossil relics are not all of the same era, and that Primary, 

 Secondary, and Tertiary periods have each their distin- 

 guishing characteristics, their own fossil relics ; that on 

 the whole the progression of life has been from the 

 lowest aquatic forms, to forms analogous to those now 

 tenanting the earth, which, when they existed in the 

 Eocene, Meiocene, or Pleiocene epoch of the Tertiary 

 period, must have presented to a certain extent the 

 superficial features it at present exhibits, though there 

 were doubtless great modifications in the arrangements 

 of land and water, and in the temperature of given lati- 

 tudes. We beg to refer our readers to the articles 

 ' Organic Remains ' and ' Geology,' in the ' Penny 

 Cyclopaadia.' The perusal will give additional interest 

 to our details of fossil relics. 



Tribe— AQUATIC PACHYDERMATA 



(The Herbivorous Cetacea of Cuvier). — If our readers 

 will turn to our account of the fossil dinotherium and 



VOL. III. G 



