30 THE CEUST WE DWELL UPON. 



Studying the preceding scheme, it will "be seen how 

 numerous are the formations that compose the earth's crust, 

 each formation representing the sediments of former lakes 

 and seas, and each varying in composition according to the 

 conditions under which it was deposited. It will further 

 be seen that from the oldest to the most recent there has 

 been an ascent, in general terms, from the lower to the 

 higher forms of life the sea-weed preceding the fern, the 

 fern the conifer, the conifer the palm, and the palm the 

 true exogenous timber-tree ; and so in like manner the 

 zoophyte preceding the shell-fish, the shell-fish the fish, 

 the fish the reptile, the reptile the bird, and the bird the 

 mammal. We have thus revealed by a study of the earth's 

 crust, what our forefathers never dreamt of namely, that 

 this crust is in a state of incessant change, what was for- 

 merly dry land becoming the sea-bed, and what was once 

 the sea-bottom being upraised into dry land ; that these 

 old sea-sediments constitute the formations which com- 

 pose the earth's crust ; that these formations are replete 

 with the evidences of former life ; that this life evinces a 

 progress from lower to higher forms ; and that all the in- 

 terchanges of sea and land, all the waste and reconstruc- 

 tion, all the growth and decay of bygone life, establish an 

 antiquity for this world of ours vast beyond all human 

 conception. 



Summing up, then, our knowledge of the rocky crust 

 and this without any conjecture as to the nature of the 

 earth's interior it may be stated in general terms, first, 

 That this rocky crust is in a state of slow but ceaseless 

 change, and that the causes meteoric, aqueous, igneous, 

 chemical, and organic that now waste and reconstruct 

 have been productive of similar changes in all time 

 past. Second, That these changes, like all other natural 

 operations, must be governed by imperative laws, and that 



