THE SECONDARY STRATA. 257 



can never have ceased, I see no means of accounting 

 for deep limestone masses unmixed with arenaceous 

 and argillaceous strata, except by considering theseas the 

 coral banks of a former earth : the present ones being 

 the obvious type of the past, as they are the only lime- 

 stone formations with which other strata cannot alter- 

 nate. And that opinion is justified by the predomi- 

 nance of corals in these ; while if they also contain 

 shells, this is no more than occurs in the present coral 

 reefs. Correlatively, where limestone beds alternate 

 much with arenaceous and argillaceous'strata, my con- 

 clusion must be, that these were formed chiefly by co- 

 lonies or beds of shell fishes ; while that opinion also 

 is sufficiently borne out by the nature of the imbedded 

 fossils. The really oolithic strata explain themselves; 

 since their present type is existing in the West Indian 

 islands. 



Of the old red sandstone I need here say nothing ; 

 having sufficiently shown that it was the produce of 

 tumultuary actions, and of ordinary deposition after 

 degradation, at a time when a new creation of orga- 

 nized beings had but commenced ; whence the rarity 

 of those in its beds is explained. The general clue to 

 the explanation of the mountain limestone is already 

 given, in the suggestion respecting coral beds, and in 

 that increase of organic beings which must be pre- 

 sumed to have then taken place ; while, when it pre- 

 sents alternating shales, the solution is not less obvious. 

 But respecting the terrestrial fossils which it some- 

 times contains, I have two suggestions to offer. Either 

 may be true, in particular cases ; while there is nothing 

 in the one that should exclude the other. 



Adopting the theory of coral reefs, it is easy to ac- 

 c'o-unt for the preserved vegetables ; since in this also, 

 an existing coral island is a type of what might or 



VOL. n. 



