A. E p 
& E ? 
bre Older Formations of T ed 
that.an equal, if not rei difforerice ftam tle ‘normal type’ 
may exist upon the two sides of the Atlantic. 4 
It is very clear that we are not to expect perfect identity ih 
T - formations at distant points, but it is ET plain, that there 
is such a general similarity that, by t of organic remains, 
we are able to decide with certainty t 16 approximate age and 
* position of any stratum ; the greater or less proportion of 
calcareous matter must, at all periods, have operated in a very 
essential manner upon the development of the corals and 
__ testacea, as we have abundant evidence in the examples cited. 
_ It is, therefore, of the first importance that the lithological 
: Deere, be studied in connection with the organic remains, 
i in order to enable one to form a correct jüdgment, in relation 
identity in the age and position of strata. We have already 
inte d to an important case of this -kind where the aug- 
ntation of calcareous matter at the west, during the period 
Of the Hudson River Group, has caused a continuation of the 
* ionii of the Trenton Limestone in great numbers, almost en- 
: z tirely to the close of that period. It is doubtless, in a great 
. degree, owing to such differences in lithological characters, 
. nd the consequent rest ng of peculiar organic forms, 
however, which have heretofore attended this comparison are 
* becoming less, and we confidently believe that when we shall 
. become bulis: acquainted with the geographical distribution 
of organic remains, and their dependence upon the lithological — 
one as the type, refusing to notice the intermediate 
i unite not only the two, but the four nominal species 
oe of the strata, we shall find little oe in x Harno 
* 
