360 CARNEGIE INSTITUTION OF WASHINGTON. 



is hence subordinate to them and subject to their partitive actions. The 

 view that the heat of the earth is mainly an inheritance which dominates and 

 restrains these processes has been abandoned. 



9. That the state of the interior of the earth as a whole is elasticostatic 

 rather than hydrostatic, but that the idiomolecular readjustments to differ- 

 ential stresses tend constantly to bring the elasticostatic condition into 

 coincidence with the corresponding hydrostatic condition, but a residual 

 divergence has always been present as far back as geologic evidences go. 



The studies of the year have involved all these propositions in greater or 

 less degree and have greatly strengthened the considerations on which they 

 rest, but only a few of these supplemental considerations need be formally 

 reported. Respecting the controlling place assigned the elastico-rigid state, 

 it is to be noted that some students of the subject have felt that, while the 

 distortional phase of the seismic vibrations traversing the earth, taken in 

 connection with the nutational oscillations and the prompt responses of the 

 earth-body to tidal deformation, leave little room to question the simple fact 

 of the elastic rigidity of the earth, yet room is left for doubt as to the effective 

 value of this property when long-continued stresses are experienced, because 

 the direct demonstrations of the elastic rigidity relate only to short stresses. 

 The studies of the year, however, show that this source of doubt is practically 

 covered by the actual phenomena, so that it is only applicable to hypothetical 

 cases. The evidence lies chiefly in two very significant facts: (1) When the 

 elastic limit of deep-lying matter is reached and a new state is inevitable, this 

 new state is most commonly a new elastico-rigid state, so assumed as to relieve 

 the enforcing stress. This is particularly the case when the balanced pressures 

 are high and the differential stresses come slowly into action. (2) The simple 

 fact that the elastico-rigid state actually exists under practically the whole 

 range of pressures, temperatures, differential stresses, and time effects now 

 being brought to bear on the various parts of the outer seven-eighths of the 

 earth, at least, as shown by the transmission of the distortional seismic waves, 

 is concrete evidence of the wide persistence and efficiency of this state. The 

 effective cooperation of the first of these features in securing the second is 

 favored by the slowness of the increase of the great stresses that affect the 

 depths of the earth-body. 



Respecting the first, it may be observed that the elastico-rigid state is in 

 itseff a yield provision of a specific kind. Its normal action under stress is 

 partitative. Half the stress is converted into strain which balances the remain- 

 ing stress; the energy thus becoming "latent." This constitutes the elastic 

 phase of the yield provision and is efficient up to the elastic Hmit, beyond 

 which the yield takes on a new phase, the existing elastico-rigid state breaking 

 down. It seems to have been assumed, without explicit consideration, that 

 this new phase must be other than elasii co-rigid, since it follows the breakdown 

 of the previously existing elastico-rigid state and since crushing, shearing, or 

 liquefaction are the common sequences in experimental work under surface 

 conditions. But glacial and metamorphic phenomena show that even at 

 relatively shallow depths of the earth, the previous elastico-rigid state is 

 followed by a new elastico-rigid state that is accommodated to the excess of 

 the existing stress and relieves it, and, further, is generally capable of sustain- 

 ing a higher stress than the previous state of like kind. This transition to a 



