300 Tlie American Geologist. Novombur, ifc9» 
It is a curious and interesting fact that, while numerous 
geologists, and especially T. Sterry Hunt and Michel Levy, 
reached the conclusion, on chemical and speculative grounds, 
that the first crust of the earth was a ferro-magnesian rock, 
only in recent times has it been possible to refer directly to 
that old crust as at present existing and svisceptible of exam- 
ination. On all hands it has been assumed that the oldest 
known rock was an acid one, represented, in Canrda, by the 
fundamental or Ottawa gneiss, which, being an alkaline-acid 
rock, has been supposed not only to represent the earliest 
magma, but the starting point in a period of magmrtic differ- 
entiation. It is necessary, on the other hand, if the green- 
stones express the character of the earliest magma, to reverse 
the process of differentiation, and to seek some way of produc- 
ing the alkaline-acid magma from the ferro-magnesian. 
These extremes of dififerentiation, or at least of difference, 
present remarkable contrasts when considered from a chem- 
ical point of view, the most noticeable of which is the occur- 
rence in one of certain elements which do not exist in the 
other, or exist in but small amounts. The "crenitic hypothe- 
sis" of Hunt was intended to explain how all the crystalline 
rocks, both acid and ferro-magnesian, could be derived from 
the earliest magma, by a long-continued process of lixiviation 
by circulating waters. Such waters were supposed to have 
brought the elements of the early magma to the surface of 
the earth and to have deposited them under circumstances 
favorable for their consolidation into all the varied rocks of 
which the Archean consists. Hunt entered into an extended 
survey of the secondary minerals of rocks, and an investiga- 
tion of their methods and sources of generation. He found 
that in a manner satisfactory to himself, all the minerals of 
the alkaline magma can be explained as derivatives from the 
ferro-magnesian magma, at least in small amounts. IJy this 
extended lixiviation Hunt believed that the original crust of 
the earth was wholly destroyed, or at least was deeply buried 
under its own ruins, and could not be anywhere identified. 
The greenstones, which, as stated, are the base of the series, 
he put into the "Huronian," and their production he consid- 
ered the last step in the process. 
Recalling, now. the principal chemical characteristic of the 
