THE EECOED. 



ROCK-FORMATIONS AND LIFE-PERIODS OF GEOLOGY. 



IN the preceding chapter we have endeavoured to lay be- 

 fore the reader a brief sketch of the PRESENT LIFE OF THE 

 GLOBE its plants and animals ; the causes which seem to 

 affect their growth ; the conditions that govern their geo- 

 graphical distribution ; their ordinal characters, as known 

 to the botanist and zoologist ; and the functions they are 

 apparently destined to perform in the economy of creation. 

 We now turn to that which is extinct to that which 

 geology exhumes from the rocky crust, and palaeontology 

 reinvests with verdure and vitality, as it clothed the forests 

 and peopled the fields and waters thousands of ages before 

 the human eye was created to be gladdened by its beauties 

 or startled by its marvels. Before we can institute a satis- 

 factory comparison, however before we can decide be- 

 tween the older and the newer, and trace tjhe order of their 

 incomings and their outgoings in the scheme of nature we 

 must first appeal to the geologist for the order, in point of 

 time, that prevails among the stratified formations. 



In the " crust" or accessible portion of the globe, we dis- 

 cover two great sets of rocks the one massive and unstrati- 

 fied, like the solidified lavas of Hecla and Vesuvius, and 

 evidently the products of igneous eruption ; the other 



