176 R. ETHERIDGE, T. W. E. DAVID, AND J. W. GRIMSHAW. 
III.—Depwctions. 
(1) As to Submergence.—It is not our purpose to enter here 
into a discussion of the general question as to whether evidence, 
such as that afforded by the submerged forest, points to a down- 
ward movement of the land or to a rise in the level of the ocean. 
A very brief summary, however, of general views held on the 
subject of beach lines will perhaps be not out of place. Of late 
years eminent geologists, notably Suess, have argued that, in the 
case of raised beaches and submerged land surfaces, the evidence 
points rather to an alteration in the level of the ocean than to a 
definite upward or downward movement on the part of the earth’s 
crust. Among causes which affect the general level of the ocean 
or distort its surface may be mentioned the following :— 
i. Development of ice masses at the Poles. 
ii. Bending of the earth’s crust. 
iii. Lateral attraction of continental masses. 
iv. Sedimentation. 
v. Position of the shore with regard to the tide wave. 
vi. Inflow of freshwater. 
vii. Difference in density of the ocean water at different localities 
due to varying conditions of evaporation, rainfall, and 
currents, 
viii. Direction of prevalent winds. 
ix. Hydration of the lithosphere. 
With reference to (i.) Lord Kelvin! has shown that the altera- 
sre in sea is during an ice age, in a non-glaciated hemisphere, 
iation of the Northern and Southern 
Henitaphiorcs was saan would amount to, (certain other pre 
mises being granted) as much as three hundred and twenty to 
three hundred and eighty feet. Mr. Warren Upham? has calcu- 
lated that during the maximum glaciation of the Ice Age in the 
Northern Hemisphere, the sea surface over the whole globe may 
1 Popular Lectures and Addresses, p. 3 
2 The Ice Age in North America—G.F. Wright, pat p. 579. 
