26 
GEOLOGY OF THE THIRD DISTRICT. 
important class of characters, whose full development, as in man, forms no part of any of 
the past known geological eras. 
Of all the characters which rocks present, there is none upon which so much reliance can 
be placed, to connect distant parts of the same country, or to connect countries even widely 
remote from each other, like those of organic remains. These bodies are all essential, and 
the chief reason why so little progress was made, excepting in local geology, was the want of 
a knowledge of fossils. In proportion to their investigation, so has our sphere of comparative 
geology extended, requiring but a few more years to complete our knowledge of the subsoil 
of the whole inhabited world. 
There is yet some skepticism as to the value of fossils as a character to determine the 
position of rocks ; and sufficient attention is not paid to the obvious fact, that the value of the 
character increases, as the knowledge of these bodies increases with the one who uses it. 
Fossils are of two kinds : those whose range is limited to one rock, mass, or short period ; 
and those whose range extends through two or more, their value depending upon their range 
being also limited, though several rocks or simple groups or formations be embraced within 
their range. 
Though all the fossils of the same era of different countries may not present specific iden¬ 
tity, yet no fact is better established in geology, than that there is identity for some of them, 
and that others are analogous only to those of the same era, being dissimilar to those of a 
different one. In any given country where a series of fossiliferous rocks exist, this is the fact, 
that on comparison with the series of another country of the same class, the same analogous 
order or sequence is observed in both. 
Since the study of the fossils which are antecedent to the Coal or Carboniferous era, in 
other words, those of the New-York system, it is well ascertained, that they cannot be con¬ 
founded with those of any other class or system; that the plants of the Coal era are pecu¬ 
liar to that era, and to none other, and so are its numerous testaceous and other marine 
fossils which are found with its limestone. The like fact is equally well established for the 
fossils of the Secondary class, which cannot be confounded with those of the Tertiary, or 
these latter with the more modern or recent ones. 
The same remarks, which apply to the classes, equally apply to the divisions of a class. 
Thus the divisions established by Mr. Murchison for the Silurian system of Wales, are readily 
recognized in New-York, showing that the same order of different kinds of fossils follow each 
other in the two countries ; leaving no doubt upon the mind of general causes having operated 
in the two countries in the same order of succession, showing a distinct fossil character for 
each division ; and not in these two countries only, but in others more widely remote, the same 
series in the same order existing in northern Russia, as ascertained on examination by the 
same distinguished geologist. 
The divisions of the Secondary class, such as the new redsandstone, the lias, the oolitic 
series, the greensand and chalk, are equally distinct from each other in their fossil character, 
and we have no difficulty in knowing to which of these European divisions our Atlantic red- 
sandstone is to be referred; or the Grypluea-, brought by Nuttall and Townsend from 
