26 II. RELICS. Introduction 



through several ages, first attained its present 

 level, f 



Obs. During this period, the less ancient and some 

 of the modern tracts ( v. . III. Soil. ) were formed ; 

 and the remains of plants and jish, as well as shells and 

 other relics of the vermes, added to the fossil world. 



Towards the middle of this period, it is probable 

 the mammalia and other land-animalsvsere either cre- 

 ated or considerably encreased in number, as their 

 remains are found, though very sparingly, in some 

 modern strata, supposed to have been deposited, just 

 before the sea had finally retired to its present limits. 



c. 11. The third period commences with the re- 

 duction of the ocean to its now actual level, and con- 

 tinues down to the present day. 



Obs. Throughout this last period, modern and 

 very recent tracts of alluvial and some other strata, 

 &c., have been deposited, and various extraneous 

 fossils, particularly the remains of the mammalia,\n- 

 troduced into the mineral kingdom. 



f The subsidence of the ocean, assumed above as a ready illus- 

 tration of our subject, is by no means contended for, as indubitably 

 established. That a gradual change, in the relative level of the 

 sea and land, has taken place, is a fact proved by numberless phe- 

 nomena; but it is of little moment in the study of extraneous fos- 

 sils, whether this change is considered as the effect of depression 

 in the water, or of elevation in the surrounded continents. In either 

 case, the same agents must have operated in the introduction of 

 organic bodies into the mineral strata, thus elevated above, or 

 abandoned by, their parent element. 



