PETROLOGICAL ABSTRACTS AND REVIEWS 363 
crust and the primordial magma” Loewinson-Lessing criticizes the results 
reached by Clarke and Washington and others as obtained by incorrect 
methods, but accepts their averages as accidentally nearly correct since 
they agree well with the mean of certain average compositions for granite 
and gabbro obtained by Daly. These latter averages seem to be accepted 
by Loewinson-Lessing as representing his primordial magmas in prefer- 
ence to any figures of his own, but they too must have been obtained 
by the methods esteemed faulty, and when one considers the different 
analyses various men would use in securing averages of “granite’’ or 
“gabbro,” or any other rock type or group, one almost wonders where the 
value of such compilations comes in. If the author’s conception of 
granite or gabbro is as peculiar as that announced for “syenite”’ one may 
well look askance at averages of his compilation. He says the mean of 
Daly’s granite and gabbro “corresponds almost exactly to the syenitic 
magma.” This mean carries 4.40 per cent MgO and 6.66 per cent CaO. 
A rock of this composition falls in subrange tonalose (II. 4.3.4) and its 
norm contains 24.2 per cent anorthite and 11.9 per cent of quartz! 
It is clear to Loewinson-Lessing that this ‘‘syenitic”’ mean represents 
two primordial magmas rather than one. This thesis is supported 
chiefly by dogmatic assertion. There is not much to convince the 
reader, for example, in his assertion that the “syenitic’’ magma could not 
be the original one “‘because the syenite is itself a derived magma.” 
Nor is it any more conclusive that the primitive monzonitic and essexitic 
magmas of Rosenbusch cannot be so regarded ‘“‘ because the monzonites 
are one of the products of the largely differentiated gabbro-syenitic 
magmas, but are not sensibly subject to differentiation.”’ Rosenbusch 
apparently does not know this and possibly he may question the 
statement! 
By equally cogent reasoning Loewinson-Lessing disposes of all other 
views as to primordial magmas and reaches four generalizations which 
may be concisely stated as follows: (1) There were two primordial earth 
magmas, of granitic and gabbroidal composition. (2) “The different 
members of the granite formation and the gabbro-pyroxenitic-peridotitic 
formation occur in much larger bodies and have a far greater development 
than other eruptives,” which is considered evidence of their primitive 
character. (3) The primordial nature of granitic and gabbroidal magmas 
is shown by abundance of facies and of associated differentiation products, 
which cannot be equally prominent with the intermediate magmas because 
they are themselves differentiation products. (4) ‘‘The original inde- 
pendence of the granitic and the gabbro-noritic formations ”’ is indicated 
