32 OP THE TRANSITION ROCKS. 
OF THE TRANSITION ROCKS. 
19. The transition are distinguished from the primitive rocks ? 
either by being made up of the rounded fragments and ruins of 
more ancient formations, or by their resting upon and covering 
rocks that are so constituted : and from the secondary, by the 
absence of organic remains, or their containing such only as be- 
long to the lower races, and more imperfect forms of animal life. 
By some geologists this division is rejected, and its members re- 
ferred to the primitive class. They divide the whole series of for- 
mations into four great classes, the primary, secondary, tertiary 
(embracing very recent deposits of sand, clay, and shells) and 
overlying, including the products of volcanoes. No very valid 
reasons are offered for the exclusion of the transition class. It 
is said that there are no fixed and manifest lines of demarcation 
and boundary, by which to separate the transition from the primi- 
tive rocks on the one hand, and from the secondary, on the other. 
But the same difficulty occurs, however numerous or few the 
classes we form. From the era of the formation of the most an- 
cient rocks, (whether by the hand of the Deity, or the agency of 
second causes) to the present time, the forces have been in 
constant activity, by which the condition of the crust of the globe 
has been changed, existing strata destroyed, and new ones formed 
and consolidated out of their ruins. There has been no interval 
of repose, the closing event of an antecedent order of things, and 
the precurser of a new ; such an epoch in the history of nature, 
that the strata formed before and after it, fall of themselves into 
classes, separated by well marked and important distinctions. 
The object of our classification of the rocks, must therefore be, 
to separate the long chain of events, reaching from the remotest 
period of time to the present day, and the effects — the rocky 
strata they have created and left behind them — into such portions 
and families as may be conveniently associated with each other. 
Geologists will differ in their views of expediency in the case, 
according to the nature of the formations about them, and with 
which they are familiar. Where the transition rocks occupy but 
a small space, they will be merged in the primitive class ; but 
where, as in North Carolina, it is the secondary class that disap- 
pears in a great measure, if not entirely, we may be excused if 
we retain the old landmarks of the science, and distribute the 
rocks into five classes, the primitive, transition, secondary, ter- 
tiary, and overlying or volcanic. 
The rocks of the transition are less distinctly characterized than 
those of the primitive class. Where, as in the case of limestone, 
argillite, and soapstone, varieties of the same simple mineral enter 
as members of the two formations, that belonging to the transi- 
tion is generally characterized by a more earthy aspect, and less 
crystalline structure. There are three or four kinds only of tran- 
