240 Notes on American Geology. 



find ample record in breccias, conglomerates, and coarse sand- 

 stones. But these formations record only the oscillations of the 

 crust at particular periods, not marking the limits of any grand 

 geological era, in which we recognize the fossilized remains of 

 a peculiar group of marine plants and animals ; and it is only by 

 the study of such groups, that we are enabled to form a system 

 of classification in strata, applicable to every region of the globe. 

 The student of geology who has mastered all the rocks and fos- 

 sils of England and Wales, limited as the sphere of observation 

 may seem, will seldom be at a loss to recognize a fossiliferous 

 formation as an old acquaintance, whether he may travel in China 

 or Peru. 



The fall of temperature (so happily illustrated by the genius 

 of Agassiz) which occurred at the commencement of the "Di- 

 luvial epoch" is so well supported by all the known facts, that 

 we feel no hesitation in applying the theory to all the inferior 

 grand formations ; indeed it gives us a clew to their obscure histo- 

 ry, without which we should study them, hopeless of penetrating 

 their mysteries, and believing their origin inaccessible to human 

 investigation. The phenomena of the " diluvial epoch" have long 

 attracted peculiar attention, from the many curious and highly 

 interesting facts which they embrace, and the great difficulty of 

 reconciling them with existing hypotheses. Enormous angular 

 masses, transported perhaps a hundred miles from the parent 

 rock, and reposing on sand or gravel which even a mill stream 

 would have swept away, bid defiance to the mighty currents 

 which so long flourished in the imaginations of certain geologists. 

 Whence came these floods, and whither did they go ? Such 

 gigantic movements would soon have restored the equilibrium 

 of the waters ; and truly they should have been busy during 

 their short reign on earth, to grind down mountains into sand, 

 roll into smoothness myriads of siliceous pebbles, plough deep 

 trenches in the solid rocks, and polish their surfaces with sand. 



The boulders rest usually on sand, gravel, or the natural soil, 

 which would necessarily have been swept away, had currents 

 transported these huge fragments, leaving them in every instance 

 reposing on indurated strata. The hypothesis of ice-floes bring- 

 ing them from the north, floating on the waters of an ocean, and 

 depositing them where they are now found, has been supported 

 by some of the geologists of the present day ; but this was in di- 



