448 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 20 
rotational and tidal forces are adequate to cause the Polflucht and West- 
wanderung of floating continents. Lambert, Epstein, and Schweydar have 
proved the insignificance of these forces. 
Wegener lays down as a principle that, during the westward migration, 
the larger continental blocks should outstrip the smaller. Yet he considers 
the less massive Americas to have moved faster than Eurasia-Africa, which 
was also left behind by the long but narrow fragment represented in the 
mid-Atlantic swell. This is but one of several inconsistencies in his reason- 
ing. 
His speculation regarding extensive wanderings of the poles encounters 
both geophysical and geological difficulties. With the earth’s axis in the 
positions given in the third edition of his book, one has trouble in accounting 
for many facts, including: the Mesozoic coals of South Africa and the Cre- 
taceous coals of British Columbia; the persistence of the Tethys and cor- 
related lands; and the postulated movement of India (which actually had 
to climb the Polflucht slope). Wegener assumes peninsular India to have 
been endowed with energy out of all proportion to its mass, but offers no 
reason for the peculiarity of this particular fragment of the Paleozoic con- 
tinent. ~ 
Wegener’s presentation of the case has provoked much discussion and 
many objections, in addition to those listed. So obvious are his logical 
inconsequences and his failure properly to weigh ascertained facts that there 
is danger of a too speedy rejection of the main idea involved.. The question 
remains whether a better statement of the hypothesis can be made in terms of: 
(1) considerable strength of the suboceanic crust as well as of the continental 
part of the crust; (2) a density of the suboceanic crust greater than the den- 
sity of the basaltic shell (substratum) immediately beneath it, involving one 
cause of crustal instability; (3) possibly a similar, though smaller, contrast 
of densities in the case of the continental part of the crust and its basaltic 
substratum; (4) the elastico-viscosity of the basaltic substratum, rigidity 
and time of relaxation increasing to a depth of about one-half of the earth’s 
radius; (5) deleveling of the continental part of the crust through a com- 
bination of oceanic pressure, the earth’s contraction, secular denudation, 
differential radioactivity, secular dimunition of the earth’s rotational velocity 
(the axis fixed), and the temporary deformation of the geoid because of over- 
thrusting. Such deleveling gives a second condition for instability. When the 
amplitudes of the crustal inequalities became large enough, a break-up of the 
Paleozoic. continent and the sliding of the fragments were compelled. The 
sliding is expected to have been directed toward the central Pacific, on all 
sides of that basin, and also directed in the sense of the meridian. (See 
two articles in the American Journal of Science, May, 1923.) 
Whether or not this sliding hypothesis can be shown to be more valid 
than Wegener’s drift hypothesis, geologists have good reason to retain the 
root idea embodied in the writings of Fisher, Taylor, and Wegener. (Au- 
thor’s abstract.) 
The concluding address, by W. D. Lampert, of the United States Coast 
and Geodetic Survey, was entitled, The mechanics of the Taylor-Wegener 
hypothesis of continental migration. 
The amount of published matter dealing with Wegener’s development of 
the hypothesis of continental migration so greatly exceeds that dealing with 
Taylor’s presentation, in spite of the latter’s priority of publication, that this 
discussion necessarily deals with Wegener’s form of the theory rather than 
with Taylor’s. 
