1 82 The American Geologist. ^^•"•^'^' i^^^- 
at Santorin which Becke has called santorinyte and alboranyte. He 
then proceeds to a similar study of certain volcanic rocks of Auvergne. 
Probably the most important part of the article is comprised under the 
caption : — "Critical examination of the theory of differentiation." The 
author states 'that this theory includes the following hypotheses:— 
"i. The terrestrial globe must have been primitively fused in all 
parts, and homogeneous." 
"2. The present heterogeneity of eruptive products must be due to 
spontaneous separations which have occurred in the original magma 
under the influence of inequalities of temperature." 
"3. Differentiation is still in progress and has continued constantly 
since the t)eginning of geological time. The general molten magma 
has divided more and more, and the partial magmas, obeying the same 
law, have divided in their turn into magmas of the second, and third 
order, etc., Thus differentiation is a normal phenomenon, subject to 
fixed rules, which circumscribe the process more and more as nature 
pursues its subterranean work." 
Certain objections to these hypotheses are then stated. 
"In the first place, nothing demonstrates the primordial homogeneity 
of the earth. If such a state had ever existed it would have been due 
either to the uniformity of composition and distribution in space of the 
cosmic materials whose precipitation and agglomeration have given rise 
to our globe, or to an energetic and prolonged mixing of the fused mag- 
ma in the earliest period of the genesis of the earth as a distinct 
planet. Now, neither of these explanations can be accepted. The di- 
versity of composition of the meteorites falling in our own times shows 
clearly that the cosmic material still in circulation in space is wholly 
lacking in homogeneity; furthermore, the study of the results of spec- 
tral analysis of the stars confirms this conclusion." * * * 
"As for the explanation of the primordial homogeneity by means of 
a supposed mixing and of the extreme fluidity of the primordial ele- 
ments of the globe, no facts support it ; it is a purely gratuitous hypoth- 
esis, and even in contradiction with what the laws of physics, mechanics 
and astronomy have led us to believe as to the destiny and rigidity of "the 
central parts of the earth, and with what is known concerning the vis- 
coscity of the fused material beneath the crust of the globe. The hy- 
pothesis of av single homogeneous primitive magma (the Urerdmagma of 
the German and Scandinavian petrographers) therefore ought to be en- 
tirely abandoned." 
The author then points out that crystallisation in a fused silicate 
magma produces only a dift'erentiation of a character essentially miner- 
alogical, and not geological. And further, that while varying specific 
gravities would tend to separate crystals in a magma, the heavier 
crystals can not descend much below their initial position without being 
redissolved on account of the higher temperature encountered. There- 
fore this process can only produce a small vertical transfer of materials. 
The theory that differentiation can be produced by the earlier crys- 
tallisation of the more basic minerals on the cooler walls of a fused 
