472 PETROLOGICAL ABSTRACTS AND REVIEWS 
ordinate the accepted principles of vulcanology with each other and with 
the truths of plutonic geology”’; and the group of conceptions advanced 
may be summarized in the name “substratum injection hypothesis,” 
since the central thesis is that all vulcanism is the consequence of abyssal 
injection. The results arrived at in many of the papers which Professor 
Daly has published during the past few years are incorporated in the 
present treatise, and his recent studies in Hawaii are especially dwelt 
upon. 
The theory postulates in the first place the existence of an acid shell 
in the earth’s crust, overlain by the sedimentary pellicle, and underlain 
at a depth of about 40 kilometers by a basaltic substratum. The latter 
conception, although perhaps the most fundamental assumption in the 
whole theory, is advanced largely without argument, it being merely 
noted that most lava is of basaltic or andesitic composition. Taking the 
existence of this eruptible substratum for granted, then, the author pro- 
ceeds to formulate the preliminary to vulcanism generally accepted as 
essential, viz., abyssal fissuring and magmatic injection. As the magma 
rises nearer the surface the great change in conditions will lead to certain 
immediate and direct consequences. In the first place, the basaltic 
magma will undergo an expansion of 1.5—6 per cent, energy being thus 
formed which may be available for opening fissures; secondly, the super- 
heat existing in the magma will probably cause the assimilation of the 
wall rock, a point more fully discussed in a well-known former paper of 
the author’s; and finally, the gases dissolved in the magma will tend to 
rise, supersaturating its upper levels, and finally separating as bubbles 
and collecting under the roof of the batholithic chamber. Emphasis 
is laid upon the necessity of defining the nature of these gases, since 
important functions are later to be ascribed to them. They are classi- 
fied as magmatic and phreatic, the former class being made up of juvenile 
and resurgent (those derived from the country rock), and the latter of 
vadose and connate (those trapped in sediments). 
The three phases of volcanic action are then fully considered. In 
fissure eruptions, which are always basaltic, the magma is highly super- 
heated, as indicated by the low angle of slope and the great length of the 
flow. That no assimilation of acid country rock has taken place must be 
due to the fact that the feeding channel is always narrow. Expansion 
of the magma and the separation of its gases as indicated above are 
doubtless features in the effusion of such floods, although orogenic action 
is probably necessary to cause the initial abyssal fissuring. The second 
phase described is one less generally considered—eruption through local 
foundering. This is conceived as taking place when the magma is of 
