THE ARCHEAN. 183 
them result from varying conditions of heat, pressure and time 
of cooling, as from alterations and metamorphism produced in 
the oldest of them after they were congealed. 
F. The opinion of American geologists is almost unanimous 
against the introduction into the nomenclature, at this time, of the 
terms Hebridian, Dimetian, or Arvonian ; though this is not 
meant to imply that if in the future convincing proofs are pre- 
sented of the existence of these series over a sufficiently large 
part of the earth, they may not then be adopted, subject to the 
ordinary rules of priority which determine questions of nomen- 
clature. 
G. There is a wide difference of opinion as to whether there 
are crystalline rocks in and later than the Paleozoic, which are 
indistinguishable from those of the Archean. It follows, there- 
fore, that there is the same difference of opinion as to whether 
lithological evidence is of any ^enera^ value in determining even 
broadly the chronological position of a rock. 
H. Specifically with regard to the Laurentian, howev^er, there 
seems to predominate the view that some of its rocks have never 
been repeated, and are thus determinable as Laurentian litholog- 
ically where present in large enough masses. 
I. Mineral constitution is not indicative of geological age, 
but it is the belief of the majority that with profounder knowl- 
edge it may one day become so. 
J. The lower crystalline rocks are: some of aqueous origin 
metamorphosed ; some of igneous origin metamorphosed. It is 
not always possible with our present knowledge to distinguish 
the one class from the other. 
K. There are evidences of life in the rocks anterior to the 
Cambrian, but not in the Laurentian. 
L. Eozoon Canadense is probably not of organic origin. 
LL. The scheme for classifying eruptive rocks which was 
formulated by Prof. Lossen and adopted by the International 
Committee for employment on the geological map of Europe, is 
not generally approved by American geologists, who regard it as 
a temporary expedient for the specific purpose mentioned, which 
should be modified as further experience shall suggest before it 
can be adopted as an universal classification. 
M. Among other reasons for modifying this scheme is its 
