384 SECTIONAL TRANSACTIONS.—C. 
Saturday, August 9. 
Excursion to the Niagara-Grimsby district. 
Monday, August 11. 
13. Joint Discussion with Section E on Changes of Sea-level in Re- 
lation to Glaciation, Continental Shelves and Coral Islands. 
(a) Prof. Reginatp A. Daty.—Delevelings connected with Glaciation 
and Deglaciation. 
Charles Maclaren, in 1842, appears to have been the first to see the importance 
of world-wide shifts of sea-level, due to the abstraction of water from the ocean to 
form the Pleistocene ice-caps. Other estimates of the maximum eustatic shift of 
this kind have been made by Croll, Tylor, Belt, Upham, Penck, Drygalski, Nansen, 
Daly, W. B. Wright, Humphreys, W. Ramsay and others. The values run between 
40 metres and about 900 metres. The most probable value is of the order of 
50 metres; that for the last important deglaciation (Wisconsin, Wirm) may be 
taken as about 40 metres. The changes of the ocean’s volume entailed elastic, and 
perhaps isostatic, deformations of the whole earth ; in consequence the range of the 
displacements of the strand-line on continental shores must have been less than the 
range registered on the deep-sea islands. 
Calculations, founded on the work of Rudzki, R. S. Woodward, Chree, G. H. 
Darwin and others, show that the deformation of the geoid by glaciation or deglacia- 
tion was too slight to be of practical significance in the strand-line problems of the 
Pleistocene period. 
The isostatic adjustments connected with glaciation and deglaciation and causing 
crustal warps seem to have been dominated by the flow of the earth’s materials at 
great depth. If so, another important part of each crustal warping was an elastic 
reaction. Further, considerable elastic distortion of the whole earth must have 
occurred during the long periods of delay in the establishment of isostatic equilibrium 
which was disturbed by the formation and disappearance of the ice-caps. The 
‘ marginal bulges’ around the ice-caps were caused chiefly by such elastic reactions. 
The collapse of these ‘ bulges’ during the restoration of isostatic equilibrium seems 
competent to explain the drowning of British forests and some other phases of 
submergence in the belt peripheral to the area of heavy glaciation in Fenno-Scandia. 
The principle of the eustatic shifts of sea-level is illustrated in a post-Glacial, 
six-metre lowering of sea-level, world-wide in its effects. New evidence of this general 
change of sea-level has been found at Saint Helena, the Cape of Good Hope, South-west 
Africa, West Africa, Bermuda, South Australia, New Zealand, Hawaii, etc.—localities 
additional to those listed in the Geological Magazine (1920). 
The relation of the last, positive, eustatic shift of sea-level to the location (drowning) 
of shore sites and delta sites of Paleolithic man is briefly discussed. The same rise 
of sea-level explains the forms and relations of the living coral reefs, the development 
of which seems to be independent of the local subsidence of the sea-floor exemplified 
in Fiji and other parts of the south-western Pacific. Emphasis is laid on the excessive 
muddiness of the sea-shores during the glacial stages and the consequent inhibition 
of vigorous reef-growth at those times. Such * mud-control’ may then have been 
even more important than temperature-control over the growth of the reef corals. 
The formation of numerous atolls and barrier reefs has been conditioned by the special 
clearness of the water on shelves and banks, the surfaces of which had been washed 
and lowered (de-graded) at the lower sea-levels of the glacial stages. There is no 
evidence that many atolls and barrier reefs ever existed in pre-Glacial time. 
(b) Prof. W. M. Davis.—Modification of Darwin’s Theory of Coral 
Reefs by the Glacial-control Theory. 
An examination of a number of reef-encircled islands in the Pacific and a 
study of all theories of coral reefs has led to the conclusion that Darwin’s theory 
of upgrowing reefs on intermittently subsiding foundations should be modified by 
