316 SECTIONAL TRANSACTIONS.—C. 
AFTERNOON. 
Excursion to Hordle and Barton. Leaders: Miss Chandler and 
Mr. E. St. John Burton. 
Tuesday, September 1. 
Mornine. 
14. Joint Discussion with Section D on Distribution of Animals in 
relation to Continental Movements. 
Dr. J. W. Evans, F.R.S.—Continental Drift. 
The distinction between the continental and the oceanic areas of the earth’s 
crust is fundamental and not as was once supposed merely the result of local elevation 
or depression. |The former consist down to a considerable depth of the light siliceous 
rocks, the ‘sial’; the latter of the heavy basic rocks, the ‘ sima,’ which also extend 
below the sial of the continents. At even moderately high temperatures and with a 
moderate content of volatile constituents, the sima is believed to yield to the action 
of continuous forces and thus allow the continents to move through it. That such 
movements have in all probability occurred is demonstrated by the remarkable 
resemblance between the rocks of Eastern South America, including the Falkland 
Islands, and those of South Africa (more especially the Cape), which are now 3000 
miles apart; a resemblance that extends over all the formations from the Devonian 
to the Jurassic and characterises their fauna, flora, lithology, glaciation, and intru- 
sive sills. These special features are also found in great part in Peninsular India, 
Australia, and the Antarctic. There would seem to have been, during late Paleozoic 
and Mesozoic times, either an extraordinary stretch of uniform conditions or a drift of 
these continental masses from one another. The fissuring indicated by faults and 
dykes in tropical and southern Africa bears evidence to a radiating tension away from 
the centre of that continent, which is what would have been expected if such 
movements had taken place. / 
Apparently there was in later Paleozoic times a vast continental massif, partly 
covered by shallow seas, which surrounded the South Pole, and extended on one side 
northwards beyond the Equator. The causes which led to the formation of this 
ancient continent, and those which resulted in its dismemberment, have yet to be 
determined. 
The terrestrial deposits of Western Europe and Eastern North America laid down 
in Palzozoic and early Mesozoic times show a similar likeness, and it seems probable 
that they too were once in much greater proximity to one another than they are at 
present, and have since drifted apart. This hypothesis is supported by the existence 
of widespread fissuring in Western Europe parallel to the ocean deeps of the east 
Atlantic, which are themselves in all probability the result of the same general drift. 
Prof. J. W. Grecory, F.R.S. 
The increasing evidence of the mobility of the earth’s crust has prepared the wa 
for a sympathetic reception of Wegener’s theory of continental drift. The lag of the 
continental masses under the influence of the earth’s rotation has been so often 
applied to the major facts of the earth structure that the Wegener extension of this 
Rg See requires serious consideration. The evidence is exceptionally varied and 
complex. 
The claim that extensive continental drift has been proved by variations of longi- 
tude in recent years is unproved ; but the method should be available for a conclusive 
test in a few years’ observations of longitude by wireless time signals. 
The lateral displacement of continents may be due to two processes—(1) variations 
in the polar flattening of the earth which would produce pressure toward or away from 
the equator, and a geographical trend along the parallels of latitude ; (2) a westward 
lag of upraised continental masses, producing meridional geographical features. 
The effects of both movements are recognisable, but not on the scale required by 
Wegener’s theory. Some evidence of western lag is accorded by the western coasts of 
