No. 398.] REVIEWS OF RECENT LITERATURE. 159 
mountain ranges and plateaus which were considerably eroded before 
the first volcanic eruptions. These eruptions throughout Tertiary 
time are conceived to have had their manifestation by a variety of 
processes, in part building up volcanic cones, in part ejecting fluid 
lavas through fissures, and in part hurling out from vents which 
have left but few traces enormous masses of brecciated volcanic rock 
in a fashion that is without parallel in any region of active volcanoes. 
This great accumulation of surface lavas was later invaded by igneous 
magn:as believed to be the elevated portions of a great complex of 
deep-seated crystalline rock; “where the underlying molten magma 
was subject to the severest pressure, the material was squeezed up- 
ward to higher levels following lines of least resistance, and consoli- 
dated at greater or less depths beneath the surface. . . . The line 
of Ishawooa intrusives marks the trend of one such upward move- 
ment of molten magma, which for the most part congealed without 
finding egress to the surface.” 
The two most remarkable features of Mr. Hague’s observations 
in the Absaroka volcanic district are the enormous mass of breccias 
and the Tertiary granites and diorites. The explanation of the 
origin of the former as from divers vents along fissures and the 
demonstration of the coarsely crystalline character of the intrusive 
stocks add new evidence to dispel the time-honored but erroneous 
notion that great cones like Ætna or Vesuvius are essential features 
of great volcanic activity, and that granite is necessarily a very 
ancient rock. The Tarawera eruption of New Zealand and the 
fissure eruptions of Iceland show that the cone is an incidental 
product of eruption, not an essential. Geikie has brought forward, 
in his Ancient Volcanoes of Great Britain, much evidence to show 
that similar fissure eruptions were the prevailing type that produced 
the Tertiary basalt plateaus, and he too describes coarse granitic 
rocks of Tertiary age. The chief point of difference in the Absaroka 
Range is in the JSrecciated character of the horizontal lavas; the 
brecciated fragments are of all shapes and sizes and of great varia- 
tion in kind, but nearly always volcanic. How did these breccias 
first crystallize as andesites or basalts in what were presumably con- 
tinuous bodies of some sort, and later become broken up? This is 
a problem that has long puzzled the Yellowstone geologists, and for 
its complete solution an extended study and comparison of similar 
tuffs and breccias throughout the Cordilleran district will probably 
be required. T. A. Jaccar, JR. 
