THE EARTH, A FAILING STRUCTURE. 
73 
behavior of the materials composing the earth ; by those who 
study the behavior of the material at the regions of failure; 
who study its mode of fracture and of flow as it fails; who 
study the relations between stresses and microscopic struc- 
ture; between pressure and density; between stresses and 
chemical condition ; between stresses and solution and re- 
deposition ; between pressure and the change of state, as 
between the gaseous, liquid, and solid conditions; between 
possible stresses in the material and its temperature; between 
stresses and the growth of crystals. 
Briefly summarized, some of the reasons for believing the 
earth to be a failing structure are as follows: If the earth is 
considered a competent elastic structure, it is found that the 
computed stresses produced hy the weight of the continents 
and mountains are so great that the existence of these stresses 
is doubtful, and therefore the assumption of competency 
doubtful. Pendulum observations and geodetic observations 
of deflections of the vertical indicate that the distribution of 
density in the earth near the surface now corresponds rather 
closely to the condition called isostasy, which is the condi- 
tion of approximate equilibrium toward which the hetero- 
geneous earth would tend if it were a failing structure. The 
approach to perfect isostasy is apparently so close as to indi- 
cate that isostatic readjusment by failure under stress has 
been going on in recent geologic time, during which there 
have been large transfers of material on the surface by erosion 
and deposition. The geologists find in the rocks abundant 
and widespread evidence of failure under stress, and evidence 
of a tendency to concentrated deformation in certain regions, 
which is a general characteristic of failing structures, in con- 
trast with the uniform and regular deformation which is a 
characteristic of competent structures. Earthquakes, ap- 
parently resulting from local failure in each case, are wide- 
spread and numerous. In the laws of frequency of earth- 
quakes in a given region there is found evidence that the 
earth is. as a rule, under stress so intense as to approach the 
breaking limit. 
11— Bull. Phil. Soc., Wash., Vol. 15. 
