SOME UNSOLVED PROBLEMS IN GEOLOGY. 287 
effect on the earth ; (2) When the rival theories are tested by the present phenom- 
ena of the southern polar region and the North Atlantic there seem to be geo- 
graphical causes adequate to account for all except extreme and unproved glacial 
conditions ; (3) The astronomical cause would suppose regularly recurring glacial 
periods of which there is no evidence, and it would give to the latest glacial age 
an antiquity which seems at variance with all other facts; (4) In those more 
northern regions where glacial phenomena are most pronounced, the theory of 
floating sheets of ice, with local glaciers descending to the sea, seems to meet all 
the conditions of the case, and these would be obtained, in the North Atlantic at 
least, by very moderate changes of level, causing, for example, the equatorial 
current to flow into the Pacific, instead of running northward as a gulf stream ; 
(5) The geographical theory allows the supposition not merely of vicissitudes of 
climate quickly following each other in unison with the movements of the surface, 
but allows also of that near local approximation of regions wholly covered with 
ice and snow, and others comparatively temperate, which we see at present in 
the north. This last consideration suggests a question which might afford scope 
for another address of an hour's duration — the question how long time has elapsed 
since the close of the glacial period. Recently the opinion has been gaining 
ground that the close of the ice age is very recent. Such reasons as the follow- 
ing lead to this conclusion : The amount of atmospheric decay of rocks and of 
denudation in general which have occurred since the close of the glacial period 
are scarcely appreciable. Little erosion of river valleys or of coast terraces has 
occurred. The calculated recession of waterfalls and of production of lake ridges 
lead to the same conclusions So do the recent state of bones and shells in the 
Pleistocene deposits and the perfectly modern facies of their fossils. On such 
evidence the cessation of the glacial cold and settlement of our continents at their 
present levels are events which may have occured not more than 6,000 or 7,000 
years ago, though such time estimates are proverbially uncertain in geology. 
This subject also carries with it the greatest of all geological problems, next to 
the origin of life, namely, the origin and early history of man. Such questions 
cannot be discussed in the closing sentences of an hour's address. 
In conclusion, science is light, and light is good, but it must be carried 
high, else it will fail to enlighten the world. Let us strive to raise it high enough 
to shine over every obstruction which casts any shadow on the true interests of 
humanity. Above all, let us hold up light and not stand in it ourselves. 
The exercises of the day and evening were pleasantly supplemented by a 
public reception by the members of the Association, under the auspices of the 
local committee, in the parlors of the Nicollet House, The reception was en- 
tirely informal. After listening to Prof. Dawson's address, the members of the 
Association proceeded to the hotel where they found awaiting them a large com- 
pany of Minneapolitans, including many leading citizens, with ladies. 
