108 
IDDINGS. 
readily fusible elementary minerals, from among the coarser 
or the less fusible, under extraordinary and locally varying 
pressures.” He considers that the partial crystallization of 
augite and feldspar in subvolcanic magmas and the previous 
processes of separation probably account for the succession 
of flows of basalt, trachyte, and clinkstone alternating with 
one another. 
In 1878 King* contributed a very important chapter to 
the question of the origin of volcanic rocks. 
By the breadth of his treatment and by better and fuller 
data he advanced the problem of the origin of the various 
kinds of volcanic rocks far beyond the point reached by any 
of his predecessors, although at the same time he was led by 
the supposed establishment of certain criteria of distinction 
to separate the so-called Plutonic rocks, including granite, 
syenite, and diorite, from volcanic rocks; so that his hypoth¬ 
esis was confined to volcanic rocks and did not include all 
igneous or eruptive rocks. 
After elaborating the order of succession of volcanic erup¬ 
tions established by Von Richthofen, so that each member of 
the latter’s order was subdivided into a hornblendic, a quartz- 
ose, and an augitic variety, which followed one another in 
the order given, he enters upon a consideration of volcanic 
fusion. After reviewing the principal theories with regard 
to the fused condition of the interior of the earth, he remarks 
that “ the greatest single difficulty which the whole theory 
of fusion has to contend with is the extremely localized 
character of its phenomena, the fact of the non-sympathy 
of adjacent volcanic regions, and the chemical diversities of 
successive and contemporaneous products.” And, having 
disposed of the hypothesis of a general molten interior, and 
of the residual lakes of Hopkins, and of the mechanical pro¬ 
duction of local lakes of fusion by Mallet, he asks, “ What 
possible cause can there be to account for those extremely 
localized and only temporarily existing pools of fusion within 
*King (C.) U. S. Geol. Exploration of the Fortieth Parallel. 4°* 
Washington, 1878. Yol. I, Systematic Geology, p. 705 et seq. 
