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 aerenniaeh whether he may travel in China 
or Peru. 
__ The fall of teaxperitare (so Jeg 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 Sep pethencs Enormous angular 
masses, transported perhaps a hundred miles from the parent 
rock, and reposing on sand or-grave] which even a mill stream 
would have swept away; -bid defiance tothe mighty currents 
which so long fl hed.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, am 
depositing them where they are now found, has been supported 
by some of the geologists of the present day ; but this was in 
