PETROLOGICAL ABSTRACTS AND REVIEWS 475 
to subordinate vulcanism. Professor Daly considers Kilauea to be 
located upon a satellitic injection or laccolith. He formulates the 
characteristics of subordinate volcanoes as follows: brief activity, 
geologically speaking, small output of lava, a cluster grouping of the 
vents rather than an alignment, and the existence of traces of surface 
deformation due to the injection of the laccolith between the strata. 
Tertiary and Paleozoic examples are probably represented in Suabia and 
Scotland. 
This theory of Professor Daly’s is thus systematic and plausible, 
granting the existence of the basaltic substratum; and his practice of 
invoking the aid of physical formulas to support his ideas is highly 
commendable. To one who has not been closely following the work of 
Professor Daly along these lines, many of the somewhat novel views to 
which he casually refers in the present paper may be startling, but the 
more obvious objections to these at least have been disposed of in the 
author’s previous articles. In a recent paper he estimates the amount 
of assimilation which a given mass of basalt can accomplish, and finds 
that about five mass-units of this rock will furnish the heat energy neces- 
sary for the solution of one mass-unit of granitic gneiss. A 5:1 mixture 
of rocks containing say 48 and 73 per cent of silica respectively would 
contain only about 52 per cent of that constituent, however, and it is 
evident that very extensive gravitative adjustment would be required to 
produce from this magma such a mass as the rhyolite flow at Yellow- 
stone Park. The conception of Kilauea as a subordinate volcano is an 
interesting one; Professor Daly might perhaps have strengthened his 
argument by a calculation of the annual loss of heat of a laccolith of 
this size, and so have arrived at an estimate of the length of time that 
it could remain molten after injection. The fact that the whole theory 
is founded largely on the study of but one group of volcanoes might 
also be urged against it, but the paper nevertheless stands as a very 
interesting and suggestive discussion of those processes whose manifes- 
tations have long been the subject of speculation to the human race. 
G. S. RocEers 
Mitcu, L. ‘Ueber Plastizitat der Mineralien und Gesteine,” 
Geolog. Rundschau, Bd. II, Heft 3 (1911), 145-62. 
Milch’s paper presents the results of various investigators on the 
plasticity of minerals and rocks with a bibliography of the literature. 
Perfect rigidity and plasticity are limiting conditions which no sub- 
stances possess. A substance is perfectly rigid when it cannot be 
deformed by any amount of stress. It is perfectly plastic when it offers 
