536 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
and clouds in the atmosphere. The steady hot rain from the atmosphere 
would rapidly disintegrate the surface rocks. Small seas and lakes of 
Water saturated with alkalies and salts would at once begin to form the 
rocks that we know as metamorpliic and archsean. The covering thus 
formed would contribute to diminish the rate of cooling of the interior 
mass, thus allowing the atmosphere to cool down to its present condition 
and deposit the most of its moisture. 
The systematic changes in the contours of the continents and the moun¬ 
tain ranges that have taken place since the Azoic period, like those that 
took place before that, have therefore not been due to any great extent 
to strains of contraction consequent on the general cooling of the molten 
nucleus of our globe, but must have been due mostly to strain produced 
by solar and lunar bodily tides, and to similar strains produced by the 
gradual slowing down of the earth’s rotation, which abatement produces 
a tendency to return from the spheroidal back to the spherical shape ; 
ancl thirdly, but to a less degree, to strains produced by the unequal cool¬ 
ing of those portions that have for a long time been continental and 
oceanic respectively. 
It will thus be seen that from our present point of view the physical 
questions involved in dynamic geology differ from those that were the 
subject of discussion a few years ago, and I should hardly have dared to 
express myself so decidedly to-night if it were not that the study of some 
problems in meteorology had forced me to go over the question as to what 
we know about the earth’s surface and its relation to our atmosphere. 
336th Meeting. April 27, 1889. 
President Eastman in the chair. 
Thirty-six members and guests present. 
Mr. C. E. Dutton read a paper on Some of the Greater Prob¬ 
lems of Physical Geology. 
Published in full in this volume, pp. 51-64. 
Remarks were made upon Mr. Dutton’s paper by Messrs. 
Woodward, Gilbert and Dutton, who have prepared the follow¬ 
ing abstracts: 
[Abstract.] 
Mr. Gilbert found difficulty in understanding the particular way in 
which the crumpling of the surface layers is produced. 
Assume a portion of the terrestrial surface sloping seaward and partly 
covered by the sea ; assume that the material near the surface is homo¬ 
geneous and sharply separated from the heavier material, also homogene¬ 
ous, beneath: then under isostacy the surface of separation between the 
