318 
Stose, A. Keith, G. I. Adams, E. T. Wherry, H. B. 
Kimmel and W. C. Alden, with replies by Joseph 
Barrell and A. W. Grabau. 
Differential Erosion and Equiplanation in Portions 
of Yukon and Alaska: DELORNE D. CAIRNES. 
(Introduced by Percy E. Raymond.) 
Certain limestones and dolomites have been 
found to offer much greater resistance to ordinary 
sub-aerial erosive agencies than most other types 
of sediments, although many of these may be con- 
siderably harder and apparently better adapted to 
withstand the destructive forces to which rocks are 
exposed. In portions of the Yukon plateau proy- 
ince, the original peneplanated upland surface has 
been almost entirely destroyed in areas in which 
the bed rock is chiefly highly metamorphosed slate 
and quartzite, but is well preserved in adjoining 
tracts where limestones and dolomites predominate. 
Where remnants of the original plateau-surface 
remain, agencies, including nivation, frost and 
chemical action are at work on the upland tending 
to remove all inequalities of the surface by trans- 
porting material from the upper to the adjoining 
lower levels; for this process the term ‘‘ equiplana- 
tion’? is proposed. This name has suggested 
itself as its results tend to make the elevation of 
all points equal in the area affected. Equi- 
planation is the reverse of peneplanation, as by 
isoplanation there is but a slight if any loss of 
material within the planated areas, but in pene- 
planated tracts all crustal matter above sea-level 
tends to become transported to the ocean. Equi- 
planation thus includes all planating activities, 
even wind action, whereby a plain-like surface 
tends to be produced, and by which there is no 
perceptible loss of material to the planated tract; 
all ordinary stream action, which is the main fac- 
tor in peneplanation, is thus excluded. 
The paper was discussed by W. W. Atwood, 
W. M. Davis, H. M. Eakin and the author. 
The Cenozoic History of the Wind River Moun- 
tains, Wyoming: L. G. WESTGATE and E. B. 
BRANSON. 
A preliminary account of the successive pene- 
planes, partial peneplanes and terraces of the 
southern part of the Wind River Mountains, the 
pre-Glacial gravels capping some of the terraces 
and the relation of the terraces to deposits of an 
earlier and a later glaciation. 
The Stability of the Atlantic Coast: Doucuas 
WILSON JOHNSON. 
The results of the Shaler Memorial investiga- 
tion of shoreline changes along the Atlantic coast 
SCIENCE 
[N.S. Vou. XXXV. No. 895 
indicate that there has been no appreciable subsi- 
dence of this coast within the last few thousand 
years. The phenomena which seem to indicate 
recent subsidence appear to fall into three groups: 
(1) Fictitious appearances of subsidence which 
are produced by wave action on a retrograding 
shore line without any change in the level of land 
or sea; to this group belong many instances of 
submerged stumps, peat exposed at low water on 
the seaward side of barrier beaches, erect trees 
recently killed by the invasion of salt water, ete. 
(2) Phenomena produced by a local rise in the 
high tide surface, due to a local change in the 
form of the shoreline, unaccompanied by any gen- 
eral change in the relative level of land and sea; 
in this group may be found examples of practi- 
cally all phenomena ordinarily attributed to a re- 
cent subsidence of the land. (3) Phenomena pro- 
duced by an actual subsidence of the land or rise 
of the sea level which occurred some thousands of 
years ago; in this group belong many of the 
deeply buried peat deposits and submerged stumps. 
The evidence of coastal stability consists of (1) 
the form and position of successive beach ridges 
the oldest of which were built by the waves thou- 
sands of years ago, yet later than the deeply 
buried peat deposits; (2) the position of aban- 
doned marine cliffs on which the waves can not 
have worked in recent time; and (3) the absence 
of a fringe of dead trees on those portions of the 
coast which are exposed neither to direct wave 
attack nor to local fluctuations of the high tide 
surface. It is concluded, with reference to the 
Atlantic coast, that the land can not have subsided 
as much as a foot within the last century; that 
there can have been no long-continued progressive 
subsidence at so high a rate as one foot per cen- 
tury, within the last few thousand years; and that 
no evidence thus far available can be regarded as 
satisfactory proof of any degree of recent subsi- 
dence, either spasmodic or progressive. 
The paper was discussed by C. A. Davis, H. B. 
Kiimmel, J. W. Spencer and A. C. Lane. 
Physiography of the Hast African Plateau: 
GroRGE L. COLLIE. 
Four physiographic regions may be recognized 
in British East Africa. First, the coastal plain; 
second, the foot plateau; third, the gneiss plateau; 
fourth, the lava plateau, which includes within its 
boundaries the great Rift Valley. The coastal 
plain is generally but two or three miles wide. It 
is composed of recent coral rock, and it is a true 
degradation plain; the agent is probably marine 
