21 



liypogean group, tliat tlicy immediately underlie and are 

 intimately associated with tlie lowest stratified schists, we 

 obtain a starting point in the crust of the earth from which 

 to obtain an intelligible description of the systems which 

 follow." 



The fact of the strictly suiface growth of every deijosit can 

 not be too strongly pressed ; every atom at the time of its 

 deposition was free to move in obedience to the waters 

 • and was left where they carried it, upon the surface, 

 until they covered it up with succeeding atoms. The geo- 

 logical strata of the earth are monuments of those parts 

 of every deposit that were thus covered away and have 

 never been used again in the formation of subsequent de- 

 posits. 



The Laurentiaii and Cambrian Systems, bearing evidences 

 of preceding and continuous heat with traces of the earliest 

 forms of vegetable and animal life — the Silurian, Devo- 

 nian, Carboniferous, Permian, Triassic, Oolitic, Cretaceous 

 and Tertiary Systems, are the remains of each deposit 

 whose surface was used by and incorporated with the 

 waters until the succeeding formation gradually covered 

 it, and saved it from further disintegration. Reaching the 

 present surface of the earth, in the post tertiary and super- 

 ficial formations, it will be necessary to learn the exact 

 relation which gaseous and liquid forms of matter bear 

 not only to the oxydation of metals and the formation of 

 hydrates, but to the development of organized bodies. 



These deposits did not, of course, all occur at regular in- 

 tervals, in regular gradation, one above the other, making 

 everything plain and easy to be understood. If it had 

 been so, the rocks and waters would have disclosed the 

 truth long since. All the complex obliterating and inter- 

 mingling forces have been at work from the first. Every 

 cause must be allowed full weight, every efiect must be 

 ^ duly considered. Nor is the action of igneous forces 

 ignored wherever its effects are evident. 



