PRIMARY, SECONDARY, TERTIARY. 
123 
The early geologists gave to all the crystalline and non- 
fossiliferous rocks the name of Primitive or Primary, under 
the idea that they were formed anterior to the appearance 
of life upon the earth, while the aqueous or fossiliferous 
strata were termed Secondary, and alluviums or other super¬ 
ficial deposits. Tertiary. The meaning of these terms has, 
however, been gradually modified with advancing knowl¬ 
edge, and they are now used to designate three great chron¬ 
ological divisions under which all geological formations can 
be classed, each of them being characterized by the presence 
of distinctive groups of organic remains rather than by any 
mechanical peculiarities of the strata themselves. If, there¬ 
fore, we retain the term “ primary,” it must not be held to 
designate a set of crystalline rocks some of which have been 
proved to be even of Tertiary age, but must be applied to 
all rocks older than the secondary formations. Some geolo¬ 
gists, to avoid misapprehension, have introduced the term 
Palaeozoic for primary, from iraXaioy, “ancient,” and “ an 
organic being,” still retaining the terms secondary and ter¬ 
tiary ; Mr. Phillips, for the sake of uniformity, has proposed 
Mesozoic, for secondary, from /xeo-oc, “ middle,” etc.; and Cai- 
nozoic, for tertiary, from Kaivog^ “ recent,” etc.; but the terms 
primary, secondary, and tertiary have the claim of priority 
in their favor, and are of corresponding value. 
It may perhaps be suggested that some metamorphic strata, 
and some granites, may be anterior in date to the oldest of 
the primary fossiliferous rocks. This opinion is doubtless 
true, and will be discussed in future chapters; but I may 
here observe, that when we arrange the four classes of rocks 
in four parallel columns in one table of chronology, it is by 
no means assumed that these columns are all of equal length; 
one may begin at an earlier period than the rest, and another 
may come down to a later point of time, and we may not 
be yet acquainted with the most ancient of the primary fos¬ 
siliferous beds, or with the newest of the hypogene. 
For reasons already stated, I proceed first to treat of the 
aqueous or fossiliferous formations considered in chronolog¬ 
ical order or in relation to the different periods at which they 
have been deposited. 
There are three principal tests by which we determine the 
age of a given set of strata; first, superposition; secondly, 
mineral character; and, thirdly, organic remains. Some aid 
can occasionally be derived from a fourth kind of proof, 
namely, the fact of one deposit including in it fragments of 
a pre-existing rock, by which the relative ages of the two 
may, even in the absence of all other evidence, be determined. 
