GEOLOGY. 361 



new state of like kind is not universally true, especially when yield by crushing, 

 shear, or melting is readily available by reason of low resistance in some one or 

 more directions, as is commonly the case at and near the surface, but as depth 

 augments the balanced stresses and distributes more evenly the differential 

 stresses, such a succession of like kind seems to become increasingly true. 

 From the particular elastico-rigid state that is overstressed and forced to give 

 way, the transition to a new state of like kind seems to take place by the 

 individual detachment of such particular atoms or molecules as are situated so 

 as to bear the most intense stress or to be held by the fewest bonds (as at 

 angles or on sharp curves) and by the transfer of these detached atoms or 

 molecules — perhaps their projection — to new points of attachment where the 

 stresses are less, or more bonds or stronger bonds are available; in other words, 

 the action is idioatomic or idiomolecular. This is not gaseous or liquid action 

 in the strict sense of these terms, for gases and liquids are assemblages, while 

 this action is individual. There may, of course, also be gaseous and liquid 

 action. The general assumption, therefore, that when an elastico-rigid body 

 yields to stress it is by crushing, shear, or liquefaction, is true only under some 

 conditions, not under all. Such methods of yield are common under surficial 

 C/vd some sub-surficial conditions. They are also prevalent when contacts favor 

 solution, or when high temperature and low pressure favor melting, but the 

 more prevalent method in the depths seems to take the form of readjustments 

 and reorganizations of the type exemplified by glacial motion and rock 

 "flowage." 



Now, having in mind this doubly adaptive mode of yielding (yielding first 

 by the elastic partition of the stress into balanced stress and strain, and later, 

 when necessary, by transformation into a new elastico-rigid state by progres- 

 sive atomic or molecular action), it is easy to understand the second very 

 significant fact, the actual elastico-rigid state of the earth in portions subjected 

 to very different combinations of balanced and differential stresses, of dif- 

 ferent temperatures, and of such effects of time as are inheritable from the 

 previous geologic ages. It is to be noted that the distortional seismic waves 

 serve as a very searching agency. They test the nature of every part of the 

 earth through which they succeed in passing. They therefore show that' a 

 highly rigid elastic state prevails very generally, if not intimately, throughout 

 the outer seven-eighths of the earth at least, in spite of the different tempera- 

 tures, pressures, differential stresses, time effects, and other cooperating 

 agencies that now exist or are represented by transmitted effects. Some 

 interstitial liquid matter and some molten pockets are of course to be recog- 

 nized. The portions shown to be elastico-rigid vary greatly in their conditions 

 and show the compatibility of the elastico-rigid state with such variations and 

 their combinations. In the light of what was said in the preceding paragraph 

 there seems no reason to suppose that any other probable variations would 

 prove incompatible. 



This combination covers essentially the whole ground of present geologic 

 action — except the subordinate states already recognized. It therefore does 

 not seem necessary to consider imaginary possibilities. 



The studies of the year have developed another very significant feature of 

 the problem of internal conditions. It is a well-known fact that rigidity and 

 elasticity increase as depth and pressure increase, notwithstanding the rise of 



