64 
HAYFORD. 
the continents to rise and fall may be due to some other 
cause than gravity. 
Lest my attitude be mistaken, I hasten to add that I have 
the highest admiration for Darwin’s paper and believe it to 
be a classic in its line. In it the assumptions are so clearly 
and carefully stated, the mathematical treatment is so broad, 
and the conclusions are so carefully expounded, so cautiously 
stated, and their relations to the possible errors in assump- 
tions so fully set forth, that the paper will stand the test 
of the most searching criticism. What has happened in the 
line of thought followed to-night has been that Darwin’s 
paper, without rejection of any essential part, has been sup- 
plemented by additional evidence, and additonal and differ- 
ent conclusions have been reached. Not a single link in 
Darwin’s chain of reasoning has been broken or damaged. 
By attaching the chain to more facts at one end, it has been 
enabled to hold up more and different conclusions at the 
other end. 
The principal conclusion reached from Darwin’s paper, 
as supplemented, is that if the material forming and under- 
lying the continents is of the same density as the material 
beneath the oceans, the earth is probably a failing structure ; 
that it is slowly yielding under the stresses, the continents 
sinking and the ocean beds rising. Please note that, on this 
evidence alone, the yielding is stated to be a probability, not 
a certainty. Because of the uncertainty, it is desirable to 
examine all available lines of evidence. 
The theory that there exists in the earth the state of 
approximate equilibrium called isostasy has an important 
bearing upon Darwin’s paper. According to the theory of 
isostasy, the material forming and underlying the continents 
is less dense than that under the oceans, whereas in Darwin’s 
computations the densities were assumed to be the same. 
Pendulum observations have long been known to indicate 
that isostasy exists. The originator of the word “isostasy,” 
C. E. Dutton, based his belief in isostasy on geologic evidence 
and pendulum observations.* Other geologists have con- 
* C. E. Dutton : On Some of the Greater Problems of Geology. Bul- 
letin of the Philosophical Society of Washington, vol. xi, pp. 51-64, 
