Introduction to Geology. 63 
the chalk. The utility of this distinction has become more 
apparent since the discoveries which the last few years have 
produced; and the arrangement is further authorised by the 
peculiar character of those numerous tribes which people these 
beds, and which were called into existence subsequently to the 
chalk. 
It was afterwards perceived that the Secondary class re- 
quired division in that part of the series wlie approached 
nearest to the Primary, or earliest-formed rocks; because 
there appeared an intermediate class, which, notwithstanding 
they contained organic remains, possessed a structure that 
allied them to the Pri imitive. On these the name of Transi- 
tion, or Intermediate, was conferred. 
There were thus founded four principal divisions of rocks, 
Primary, Transition, Secondary, and Tertiary. M. Al. de 
Humboldt adheres to this order in his Table of Geological 
Formations, which enriches the work of Baron Cuvier ; “and 
most Continental and English geologists pursue the same 
system. 
Werner, the celebrated mineralogist of Germany, divided 
the formations into Primary and Floetz only, which latter in- 
cludes the Transition and Secondary. Mr. Weaver and Dr. 
Macculloch have adopted a similar arrangement in their clas- 
sification of rocks. 
Mr. Coneybeare, in his admirable Introduction to the Geo- 
logy of England and Wales, makes use of another system, 
pe ded on the position of the strata and rocks, under five 
heads: 1. Superior order; 2. Supermedial order; 3. Medial 
order ; 4. Sub-medial order ; 5. Inferior order. This arrange- 
ment has the single recommendation of being divested of all 
theory. 
The first is the Tertiary class above mentioned, or that which 
Werner named the Newest Floctz class; the second is the Se- 
condary class, the Floetz of Werner, and the Sedimentary of 
others ; the third and fourth comprise the Transition, or inter- 
mediate class ; and the fifth the Primitive, or Primary Rocks. 
From its apparent want of perspicuity, this mode of classi- 
fication will not, probably, be so often used as the four divi- 
sions before adopted. Notwithstanding it is allowed that no 
such distinctions as primary, secondary, ‘and tertiary absolutely 
exist in natur 5 and that there is no imperative necessity | for 
applying such terms, it is maintained that the system is ex- 
tremely convenient and intelligible, and that it ought to be 
continued ; at all events, that we are justified in using it until 
some one can contrive a better. 
Without entering into a disquisition on the comparative 
