JuLY 30, 1897.] 
the encircling ranges was transformed into 
the present Park Plateau by the extravasa- 
tion of immense flows of rhyolite of Pliocene 
age. Still later the recent basalts, the last of 
the igneous extrusions, poured out over the 
rhyolite along the ridges of the plateau. A 
vertical section accompanies the text, showing 
the order of succession of the extrusive flows 
from the earliest outbursts to the final dying- 
out of eruptive energy. It is shown that long- 
continued currents of heated waters and acid 
vapors have acted as powerful agents in de- 
composing the igneous rocks of the plateau, and 
date back to Pliocene time; at least they were 
active before glacial ice covered the country. 
Hot springs, geysers and solfataras are closely 
associated with the rhyolite, and in fact thermal 
activity is confined almost exclusively to areas 
of this rock. 
The illustrations relate mainly to the occur- 
rence of both active and dormant geysers and 
hot springs, or some phase of volcanic geology. 
The Grand Caiion, well shown in the illustra- 
tions, is a profound gorge cut in the Pliocene 
rhyolite, the brilliant coloring being due to the 
action of thermal waters. 
‘An Illustrated Flora of the Northern United States, 
Canada and the British Possessions. By NA- 
THANIEL LORD BRITTON and Hon. ADDISON 
Brown. Volumell. Portulacacez to Men- 
yanthacee. New York, Charles Scribner’s 
Sons. Pp. 648. $3.00. 
The elaborate review of the first volume of 
Britton and Brown’s ‘Illustrated Flora of the 
Northern United States,’ which was given by 
Professor Conway MacMillan in ScrENCcE, ren- 
ders necessary only a brief notice of the second 
volume, which has now appeared. 
Following the Engler and Prantl sequence, 
the first volume was made up chiefly of the 
monocotyledonous plants, which, compared 
with the other large groups of flowering plants, 
are probably the least attractive. In the present 
volume are included such large and well-known 
families as the Pink family, Crowfoot family, 
Mustard family, Rose family, Pea family, Car- 
rot family, and the Heath family. As a whole 
the volume exceeds in interest and attraction 
the earlier one. 
9 
SCIENCE. 
179 
In running through the book a leading fea- 
ture of excellence impressed upon one is that 
there are brought together here for the first 
time in a systematic manner the results of all 
the recent scattered special papers on our North- 
eastern plants. For example, the critical work 
done in the past few years on Amelanchier Cana- 
densis, Cardamine hirsuta, Ranunculus repens 
and Agrimonia Eupatoriais here found carefully 
collated and systematized, full consideration 
being given to the conclusions of those who 
have done the work and whose opinions are 
therefore most to be depended upon. 
A liberal view has been maintained regarding 
the delimitation of species, the work in this re- 
spect standing alone among our recent manuals. 
There has been a tendency among our manual 
writers, in case of any difficulty in the definition 
of specific types, to follow the antique British 
method of giving up any attempt at segregation 
and putting a number of diverse forms under 
one name. ‘The results of the endeavor to give 
full consideration to valuable critical work is 
exceedingly gratifying, and will certainly serve 
to encourage in botanists habits of close obser- 
vation on our supposedly well-known Hastern 
flora. No better example of judicious segre- 
gation could be cited than the separation from 
the old Ranunculus repens of three additional 
species, R. septentrionalis, R. hispidus and R. 
macounit. 
In the matter of generic treatment this vol- 
ume gives a similar impression of liberality, the 
limitation of genera corresponding very closely 
in this work with that of continental European 
authors. As extreme examples of the extent 
to which the generic segregation has been car- 
ried may be cited C£nothera, which is here 
divided into eleven genera. It is clearly a 
recognized principle throughout the work not 
merely that a genus is a group which can 
always be recognized by some one or more in- 
variable technical characters fitting nicely in a 
key, but that it isa group of plants which re- 
semble each other in what is perhaps best rep- 
resented in English by the word style, and that 
the question of an arbitrary mark, as it were, is 
of secondary, not of primary importance. 
The drawings, for which the book is most 
likely to be criticised by botanists of critical 
