JULY 9, 1897.] 
To a wise and prudent man no chapter could 
be more embarrassing and disagreeable to write 
than this one. In truth, the science has no 
newly established inductions to record which 
help to solve this mystery. It is just where it 
stood twenty years ago. 
But if the second chapter is unsatisfactory by 
reason of the obduracy of the subject and the 
lack of progress to announce, the third and 
fourth chapters are the reverse. In these are 
described the materials brought by eruptions to 
the surface and their modes of occurrence. 
Along this line there has been great and rapid 
progress and our knowledge is fast taking shape. 
Since the time of Sorby the petrographer’s 
microscope has yielded a world of knowledge 
of the constitution of rocks and opened the 
way to the solution of many questions. The 
field observation of erruptive material has also 
become more accurate and discriminating. The 
author’s treatment of the whole subject, though 
brief and much condensed, is admirable. The 
field geologist of long experience among the 
volcanics will keenly realize the practical and 
accurate way in which every important feature 
is described and its significance interpreted. 
As we read it, it all seems simple enough. But 
it is that simplicity which is the result of great 
knowledge and experience, clarified by many 
years of laborious thought and frequently re- 
vised expression of it in writing. Especially 
gratifying is the broader or primary basis of his 
classification of the lavas. It is the strictly 
chemical one and there should be no other. In 
fact, most geologists have now adopted it by 
common consent. The classification by con- 
tained minerals and texture can only be second- 
ary and subsidiary. In the earlier stages of 
microscopic petrography there was an apparent 
tendency on the part of many able investigators 
to make everything turn upon mineral contents 
and it proved to be a serious clog upon the re- 
sults of their researches. New facts in extra- 
ordinary abundance, and many of them of high 
import, were brought to light, but the methods 
of grouping them often selected rendered them 
barren of generalizations. It is a matter of 
vast importance how we group volcanic rocks, 
for it profoundly influences the directions and 
limitations of our speculations concerning their 
SCIENCE. 
65 
genesis and primitive condition within the earth. 
The descriptions of the rock textures, their 
appearance to the naked eye and in the micro- 
scope, and the explanations of the terms which 
are commonly used to designate their many 
varieties, are all excellent and the examples 
well chosen. The descriptions of lava sheets 
follow. The clastic volcanic materials, con- 
glomerates, agglomerates, tuffs and volcanic 
dust are given careful and accurate attention. 
The finer material is worthy of especial study 
in this country, where it has not hitherto been 
followed up with the diligence it deserves. 
The fourth chapter is devoted to the especial 
consideration of materials errupted at the sur- 
face and to the types of volcanic piles, three 
types being taken, the Vesuvian, the Plateau 
or fissure and the Puy types. 
The fifth chapter deals with the underground 
phenomena, the vents themselves and the necks 
or cores left in the passageways of the lavas to 
the surface being described with great fullness. 
It is a favorite theme of the author and he in- 
vests it with the liveliest interest. 
The next, or sixth, chapter treats of dykes 
and the subterranean intrusive masses in the 
forms of laccolites and sheets of lava forced in 
between sedimentary beds. Finally he discusses 
those remarkable and singularly interesting in- 
trusions named bosses, which are often so puz- 
zling and hard to understand and which look 
as if a vast mass of relatively soft or plastic ~ 
material had been trying to punch an immense 
hole or passageway upwards through hard, 
rocky strata and at the same time to preserve 
its identity and general shape with compara- 
tively little deformation. This paradox is often 
seen in our Western mountains and is the prob- 
lem of the so-called dome structure and erup- 
tive granite of California and Colorado. 
The remainder of the work, and much the 
greater part of its bulk, is a detailed descrip- 
tion of the volcanic relics of the British Islands. 
It begins with the eruptions of the Archean and 
ends with those of the Tertiary. The whole 
mass of material is arranged so as to constitute 
a geological history of vulcanism and also so as 
to show it in its relations to the geological 
evolution of the land. It is not light reading 
and is not a study for children. But to the ex- 
