HYPOTHESIS AND DEFINITIONS. 



25 



HYPOTHESIS. 



The hypothesis here proposed will not explain the several ^^j^f ^JoH'^. 

 advances and retreats of salt and fresh water, the latter on plain fresh 



and salt wa- 



dry land of course. It is true, we are authorized to suppose ter altera- 

 large cavities formed in the earth by the elevation of rocks, 

 which would receive much water. We may imagine, that 

 these rocks fell back more or less, and were raised again, 

 several times in succession ; and that the water would enter 

 into, and return from, these cavities, at every such change. 

 But we have no conclusive evidence of such wonderful change- 

 es. 



Other hypothesis, of equal plausibility and equally void of 

 demonstrative support, might be proposed. But, though many 

 phenomena may now be explained, more facts must be collect- 

 ed before tenable theories can be proposed. 



The characters and relative ages of geological depositions, Ages of 

 whether we call them strata, formations, series, or classes, 

 must be studied in their individual and collective states. It 

 appears most expedient to present the first view of them under 

 the general heads, of classes or series, 



DEFINITIONS OF CLASSES, 



Classes, 



Of Regular Deposites. 



Class i. Prhnitim Class, or First Series, includes those 

 rock strata, which never contain organic relics, and never re- relics, 

 pose on rocks which do contain such relics. 



Class ii. Transition Class, or Second Series, includes Oldest 

 those rock strata which contain animal and vegetable relics : ""f^^'^* ' 



o cnamberecl 



but the animal relics are always of the radiated kind, or mol- i"ollusci. 

 luscus with more than one valve, or one-valved and (generally 

 if not always) chambered ; and the vegetable relics are mostly 

 acotyledonous and stiped — rarely monocotyledonous and cul- 

 miferous.. 



Class hi. Lower Secondare/ Class, or Third Series, in- Univalves 

 eludes those rock strata which, in addition to the relics of the bered?"^ 



4 



