Origin of the ArcJiemi Igneous Rocks. — Wincliell. 299 
Devil's Heart hill, 175 feet high, in North Dakota, could be 
formed within a few }ears for an}' single section, or perhaps 
even within one summer for the great kame mentioned. 
Some of these gravel-depositing rivers, as shown by the 
widths of esker ridges and plateaus, were two to five or ten 
times larger than those of the moulins and rock kettles. 
THE ORIGIN OF THE ARCHEAN IGNEOUS ROCKS. 
By N. H. WiNCHELL, Minneapolis, Minn. 
It has been shown by the writer in a previous paper* that 
the greenstones of the Archean are the oldest known rock, 
and may safely be considered, in our present state of knowl- 
edge, as the existing representative of the original crust of the 
globe. This, of course, leads to the necessity of admitting 
that the primordial magma was a ferro-magnesian one, at least 
so far as it existed at the surface of the cooling globe, and it 
would be also reasonable to admit that igneous rocks of later 
date, having the same composition, were derived from the 
same magma from deeper points within the earth. With this 
for a point of departure, it becomes necessary to inquire into 
the origin of the alkaline magma which gave rise to the gran- 
ites and igneous gneisses. 
It w^as likewise shown in a previous paper that the granitic 
magma made its appearance amongst the rocks of the earth 
at a later date than the ferro-magnesian, since the oldest alka- 
line rocks occasionally intrude into the oldest ferro-magne- 
sian. 
These two types of Archean igneous rock may be accepted 
as the dominant great facts in Archean vulcanology, and all 
subordinate facts may be considered as attendant and acci- 
dental, but yet legitimate, consequences of the reign of these 
two. This statement necessarily covers the occurrence of 
igneous rocks of intermediate characters. They must be con- 
sidered as in some way dependent on the leading role played 
by the greater agents, and as unimportant in a fundamental 
inquiry into the origin and mutual relations of those greater 
agents. 
*Am. Geol. Oct., 1898, p. 262. 
