ey
emerged from beneath the water.

But, on the other hand, we observe in certain formations now in
progress, particularly in coral reefs, and in deposits from the waters
of mineral springs, both calcareous and siliceous, that the texture of
rocks may sometimes be stony from the first. This circumstance may
account for exceptions to the general rule, not unfrequently met with,
where solid strata are superimposed on others of a plastic and
incoherent nature, as in the neighborhood of Paris, where the tertiary
formations, consisting often of compact limestone and siliceous grit,
are more stony than the subjacent chalk.

It will readily be understood, that the various solidifying causes,
including those above enumerated, together with the pressure of
incumbent rocks and the influence of subterranean heat, must all of them
require time in order to exert their full power. If in the course of
ages they modify the aspect and internal structure of stratified
deposits, they will give rise to a general distinctness of character in
the older as contrasted with the newer formations. But this distinctness
will not be the consequence of any original diversity; they will be
unlike, just as the wood in the older trees of a forest usually differs
in texture and hardness from that of younger individuals of the same
species.

_Transition texture_.--In the original classification, of Werner, the
highly crystalline rocks, such as granite and gneiss, which contain no
organic remains, were called primary, and the fossiliferous strata
secondary, while to another class of an age intermediate between the
primary and secondary he gave the name of transition. They were termed
transition because they partook in some degree in their mineral
composition of the nature of the most crystalline rocks, such as gneiss
and mica-schist, while they resembled the fossiliferous series in
containing occasionally organic remains, and exhibiting evident signs of
a mechanical origin. It was at first imagined, that the rocks having
this intermediate texture had been all deposited subsequently to the
series called primary, and before all the more earthy and fossiliferous
formations. But when the relative position and organic remains of these
transition rocks were better understood, it was perceived that they did
not all belong to one period. On the contrary, the same mineral
characters were found in strata of very different ages, and some
formations occurring in