CHAPTER II. 



THE DIFFERENT AGES OF STRATIFIED FORMATIONS. 

 THEIR SUCCESSIVE DEPOSITIONS. 



THE next point to be considered is Are stratified 

 rocks of different ages ? They are, and the diagram, 

 fig. 1, p. 13, will help to make this clear. There the 

 bed No. 1 must be the oldest, because it was deposited 

 in the sea (or other water) before bed No. 2 was 

 laid above it as layers of mud, and so on to 3 and 4 

 taking the strata in order of succession. But that 

 is not enough to know. We are anxious to under- 

 stand what is the actual history of the different stages 

 which such minor beds represent, Now, if we had 

 never found any fossil remains imbedded in the rocks, 

 we should lose half the interest of this investigation, 

 and our discovery, that rocks are of different ages, would 

 have only a minor value. Turn again to the diagram. 

 We find at the base, beds of limestone, No. 1, perhaps com- 

 posed of corals and shells. The organic remains in the 

 upper part of these beds lie above those in the lower part, 

 and therefore the latter were dead and buried, before the 

 once living shells which lie in the upper part inhabited 

 the area. Above the limestone lie beds of shale, No. 

 2, succeeded by No. 3, a conglomerate, and then comes 

 the bed of sandstone, No. 4 ; therefore the shells (if 

 any) in the bed of shale, No. 2, are of younger date 



