OBLITERATED CONTINENTS. 135 



extensive sandstone' formations, which underlie whole coun- 

 ties, which underlie, or have underlaid, states broad 

 enough for an empire. 



How few of us have reflected in this direction. The 

 very rocks which underlie Chicago or New York are a pile 

 of ruins. Everywhere, the rocks are almost universally 

 old material made over, who can say how many times 

 made over? The geologist formerly discoursed of fire- 

 formed rocks; and regarded granite and its associates as 

 rocks that had assumed their present condition from a 

 state of fusion. Now we are persuaded that granite, like 

 sandstones, has had a sedimentary origin. It was once a 

 mass of sand and mud upon a sea-bottom. Heat has sub- 

 sequently baked the materials, and almost obliterated the 

 ancient lines of stratification. The rocks now admitted 

 to be of igneous origin are few. Only ancient and mod- 

 ern lavas are fire-formed rocks. 



How vast, then, has been the destruction of the land in 

 ancient times! The entire mass of the solid crust of the 

 earth save only the lavas must be taken as the meas- 

 ure of the wastage or denudation of the older lands. 

 Reflect upon the thickness of these strata, reaching, per- 

 haps, a hundred thousand feet, and enwrapping the entire 

 globe. Only the oldest layers or formations are absolutely 

 continuous; and the very newest occur in patches of limited 

 extent; but the newer as well as the older underlie all the 

 seas, and the mean thickness is so vast as to convey a vivid 

 idea of the amount of work which has been done by geo- 

 logical agencies in diminishing, or even obliterating, conti- 

 nental masses whose sites are now lost, or known only 

 from surviving vestiges. 



Tt is an interesting thought, an impressive thought, 



