PETROLOGICAL ABSTRACTS AND REVIEWS 365 
“What origin have the igneous rocks and why are they represented 
by the same types in all periods?” is the third question discussed. 
Loewinson-Lessing believes in a fluid nucleus, that no trace of the 
primordial crust remains, that all magmas of rocks were derived by the 
fusion and refusion of the crust, principally from its lower surface. As 
the materials are always the same worked over and over again, the range 
of composition cannot change except that probably extreme products 
will become more abundant with time. Theory and speculation run 
persistently all through this discussion unbridled by too close connection 
with fact or formulated laws. The following quotation (p. 254) seems to 
indicate the author’s point of view: ‘We take it as a fact that there must 
be admitted two independent primordial magmas, while all other eruptive 
rocks are derivates from them, originating by assimilation and differ- 
entiation. Such a hypothesis is based on the following facts and 
considerations.” The italics, inserted by the reviewer, serve to illustrate 
the lack of distinction between fact, theory, hypothesis, and opinion 
prevailing in the discussion and markedly decreasing its value. 
It is worthy of comment that Loewinson-Lessing does not go to the 
root of the matter by considering the origin of the “primordial”? magmas 
assumed by him and their relation to the earth as a whole. Nor does he 
touch the great problems to which Harker gives his attention. 
The special theme of Harker’s address is ‘the geographical aspect of 
petrology,” introduced by a review of the geographical distribution of 
igneous rocks. Then comes a discussion of ‘“‘the alkaline and calcic 
branches” and of “the relation between tectonic and petrographical 
facies.” The latter is illustrated by references to the relations existing 
in the north British Tertiary province, as worked out by Harker. The 
bearing of the considerations presented on petrogenesis and systematic 
petrography is taken up briefly in conclusion. 
The aim in Harker’s address, as in his valuable and interesting work 
on the Natural History of Igneous Rocks, is plainly to contribute to a 
logical interpretation of the known facts and relations of igneous rocks. 
This should be the ambition of every petrologist, yet in the succeeding 
comments on this address the reviewer’s wish is to give point to his own 
belief, in which he is not alone, that some of the great -generalizations 
accepted by Harker, and many with him, are not yet sufficiently in accord 
with the facts to serve the uses made of them. In the desire to elucidate, 
what is in its essence most complex and elusive, the experience of the ages 
with premature or hastily formulated hypotheses must not be forgotten. 
