THEIR ROCK-FORMATIONS. 203 



into eocene, miocene, and pliocene, if we take, as Sir Charles 

 Lyell has done, the relative proportions of recent and fossil 

 shells which occur in the successive stages.* But whatever 

 the nomenclature we adopt, it is clear that the clays, sands, 

 gravels, marls, limestones, gypsums, and lignites which con- 

 stitute the tertiary system are the varied sediments of lakes, 

 estuaries, and shallow seas; and that in general the extent 

 and boundaries of these areas of deposit are more apparent 

 than those of the earlier systems. Indeed, many of the 

 tertiary deposits occupy limited spaces in the existing 

 continents, and thus we are led to infer that something 

 like the present distribution of sea and land had then begun 

 to prevail. At all events, much of the existing dry land 

 was then above water, and supplied the material for the 

 sediments, as well as the habitats for the terrestrial flora 

 and fauna of the period. Of course, it is not contended 

 that the continents had then assumed their present outlines, 

 nor that many lands then existing are not now submerged ; 

 but it is indicated that there is considerable relationship 

 between Tertiary and Recent times, and that the fossils of 

 the Old World tertiaries are more akin to the living plants 

 and animals of the Old World than to those of the New ; 

 while, on the other hand, the tertiary fossils of the New 

 World bear a striking resemblance to the plants and 

 animals that still flourish there. In other words, we are 

 approaching in tertiary times more nearly to the existing 

 ordainings of nature, and may therefore expect a closer 



* Taking a hundred shells from the lower, a hundred from the middle, 

 and a hundred from the upper tertiaries of the London and Paris "basins, 

 Sir Charles found that only a small percentage (3 to 5) of existing species 

 occurred in the lower, hence eocene (Gr. eos, dawn ; Jcainos, recent), or 

 dawn of existing things ; that the number of existing species was some- 

 what less than the extinct (25 to 40) in the middle, hence miocene (meion, 

 less), that is, less recent than the existing ; and that in the upper the ex- 

 isting species exceeded the extinct (70 to 90), hence pliocene (pleion, more), 

 that is, more recent than the middle or lower divisions. 



