110 
ELEMENTS OE GEOLOGY. 
disturbing the original position of rocks, and the other in de¬ 
stroying large portions of them, for our power of consulting 
the different pages and volumes of those stony records of 
which the crust of the globe is composed. Why, it may be 
asked, if the ancient bed of the sea has been in many regions 
uplifted to the height of two or three miles, and sometimes 
twice that altitude, and if it can be proved that some single 
formations are of themselves two or three miles thick, do we 
so often find several important groups resting one upon the 
other, yet attaining only the height of a few hundred feet 
above the level of the sea ? 
The American geologists, after carefully studying the Al¬ 
leghany or Appalachian mountains, have ascertained that 
the older fossiliferous rocks of that chain (from the Silurian 
to the Carboniferous inclusive) are not less than 42,000 feet 
thick, and if they were now superimposed on each other in 
the order in w^hich they were thrown down, they ought to 
equal in height the Himalayas with the Alps piled upon 
them. Yet they rarely reach an altitude* of 5000 feet, and 
their loftiest peaks are no more than 7000 feet high. The 
Carboniferous strata forming the highest member of the se- 
ries, and containing beds of coal, can be shown to be of shal¬ 
low-water origin, or even sometimes to have originated in 
swamps in the open air. But what is more surprising, the 
lowest part of this great Palaeozoic series, instead of having 
been thrown down at the bottom of an abyss more than 
40,000 feet deep, consists of sediment (the Potsdam sand¬ 
stone), evidently spread out on the bottom of a shallow sea, 
on which ripple-marked sands were occasionally formed. 
This vast thickness of 40,000 feet is not obtained by adding 
together the maximum density attained by each formation 
in distant parts of the chain, iDut by measuring the succes¬ 
sive groups as they are exposed in a very limited area, and 
where the denuded edges of the vertical strata forming the 
parallel folds alluded to at p. 87 “crop out” at the surface. 
Our attention has been called by Mr. James Hall, Palaeon¬ 
tologist of I^ew York, to the fact that these Palaeozoic rocks 
of the Appalachian chain, which are of such enormous den¬ 
sity, where they are almost entirely of mechanical origin, 
thin out gradually as they are traced to the westward, 
where evidently the contemporaneous seas allowed organic 
rocks to be formed by corals, echinoderms, and encrinites in 
clearer water, and where, although the same successive pe¬ 
riods are represented, the total mass of strata from the Silu¬ 
rian to the Carboniferous, instead of being 40,000 is only 
4000 feet thick. 
