PETROLOGICAL ABSTRACTS AND REVIEWS 367 
well known to need recapitulation.”” The arbitrariness of referring a 
host of rocks of intermediate composition to one or the other of these 
undefined classes is not acknowledged. Exceptions are called 
“‘anomalies’”’ and treated as of no moment. It is said that “A given 
province is either of calcic or of alkaline facies, typical members of the 
two branches not being found together.” This may be true if a province 
is not a province when it has mixed characters. Again, it is said that 
“it is possible to map out the active parts of the earth’s crust into great 
continuous regions of alkaline rocks on the one hand and of calcic rocks 
on the other.”’ That may be true if numerous “‘anomalies”’ are dis- 
regarded and given a free hand in mapping through absence of criteria 
really distinguishing the branches. 
The interesting generalization most dwelt upon by Harker is expressed 
in these words, “The distribution of different kinds of rocks is seen to 
stand in unmistakable relation to the leading tectonic features of the 
globe.’”’ As here stated most petrologists of experience may agree with 
the author, for he merely says ‘different kinds of rocks” and does not 
specify the relation. In truth all the essential elements of this relation 
are still to be determined by careful study of many districts. When 
- Harker jumps to the further conclusion that the significant relation is 
between the two branches of magmas and the different kinds of stresses 
producing folding or faulting of the crust, he goes far into the realm of 
hypothesis. That his devotion to this hypothesis leads him into appar- 
ently forced interpretation of admitted facts seems abundantly illustrated 
by his own sketch of the relations of the alkaline and calcic branches in 
the north British Tertiary province. 
In this area of various epochs of eruption Harker is confronted with 
the necessity of explaining a provincial mingling of alkaline and calcic 
rocks. This is accomplished to his own satisfaction by postulating 
changes in the fundamental character of underlying magmas in harmony 
with the tectonic history, faulting having predominated in certain epochs 
in which alkaline rocks are thought to play the active réle, while folding 
at other times is accompanied by the appearance of the calcic lavas. 
The difficulties of this situation are numerous in any case. Basalts 
of puzzling associations are placed in the alkaline branch because of 
sodic zeolites which are thankfully recognized as really primary and a 
most important part of the magma, since through them the alkaline 
nature of the basalts can be determined. (This idea, if correct, may be 
conveniently applied to determine the primary or secondary origin of 
alkalic zeolites. In a basalt of a calcic series of lavas such zeolites are 
