396 
Appalachians, are signalized; the first having 
witnessed the obliteration of the ancient moun- 
tains of deformation in the production of an 
extensive peneplain; the second, introduced 
by general aplift, sufficing to produce strips of 
peueplain on the weaker rocks, but leaving the 
harder rocks so little worn that their skylines 
suffice to guide the restoration of the earlier 
plain ; the third, introduced by an uplift of less 
amount, a relatively brief episode up to to-day, 
inasmuch as it has permitted only the erosion 
of narrow valleys in the floor of the weak-rock 
intermont peneplains. Pauses in the later up- 
lift are indicated by rock terraces on the sides 
of the young valleys ; the recency of the latest 
uplift is proved by the occurrence of ungraded 
riffles of hard rock in the beds of the larger 
streams. The meandering courses of the young 
valleys in their longitudinal parts are thought 
to have been inherited from free meanders de- 
veloped on the open floors of the intermont 
peneplains, before their upheaval. Several ex- 
amples of stream adjustment are presented. The 
report includes many excellent plates ; the view 
of Cumberland and the notch in the even- 
crested Wills mountains being most character- 
istic of Allegheny scenery. The report is 
accompanied by an excellent atlas of six map- 
sheets ; three delicately contoured topographic 
sheets ; and three with an overprint of geologic 
colors on the topographic base. 
The author of the above chapter remarks 
that the modern method of studying the topog- 
raphy of a district ‘seeks, from a study of the 
outward forms, to discover the reasons for 
their existence and the processes by which 
they have been produced. * * * The present 
physiographic study of Allegany county aims 
to so present its topography and topographic 
development as to make clear the reasons why 
the county has the surface features which 
characterize it.’ A somewhat different word- 
ing would have expressed a shade of mean- 
ing which is believed to be more appropriate 
physiographic chapter, namely, ‘this 
physiographic study of county presents 
the reasons for the existence of the local topo- 
graphic forms and the processes by which they 
have been produced in order that the forms 
themselves, as they now exist, shall be better 
to a 
SCIENCE. 
[N.S. Vou. XIII. No. 323. 
known.’ The processes of the past are in 
themselves essentially of a geological nature ; 
they gain a relation to physiography only 
when they illuminate the facts of the present. 
Their value to the physiographer lies in the 
power that they give him to see and to describe 
the existing facts of topographic form, for 
physiography is essentially a study of present 
conditions. 
THE PHILIPPINE ISLANDS. 
G. F. BECKER contributes a ‘ Brief Memoran- 
dum on the Geology of the Philippine Islands’ 
(20th Ann. Rep. U. S. Geol. Surv., pt. ii, 1900, 
1-7), which gives another kind of illustration 
of the point just made regarding the illumina- 
tion of the present by the past. 
Although strictly geological in having to do 
with past process and time, the essay has a great 
physiographic value in aiding the imagination 
to build up a conception of present forms. A 
strong deformation and uplift of Eocene and 
older strata was followed by extensive denuda- 
tion. This was later accompanied by depres- 
sion, which reduced a large land area to a 
group of small hilly islets. Volcanic eruptiens, 
making vast additions of material to their de- 
nuded and submerged foundation, began dur- 
ing this submergence; then came a general 
emergence which, with eruptions, has continued 
ever since; Mayon, one of the most symmet- 
rical cones in the world, having had a violent 
eruption in 1897. The emergence of the re- 
gion has revealed coral deposits of the shore 
waters, which make nearly continuous mantles 
far up the land slopes, even to altitudes of 2,000 
feet. Pauses during uplift allowed the waves 
to carve sea cliffs and benches, which now take 
the form of terraces, more or less dissected, 
as one of the most prominent topograph- 
ical features of the islands. The last hundred 
feet of uplift have revealed extensive lowlands, 
the most valuable part of the archipelago. 
Considerable areas have been added in deltas, 
where the mangrove and the nipa palm aid in 
the deposition of river sediments. 
OVERDEEPENED ALPINE VALLEYS. 
KILIAN, of Grenoble, dissents from the opinion 
that the overdeepening of glaciated Alpine 
valleys and the associated discordant mouthing 
