GEOLOGY. 423 



as to be able to grow. Such a simple detachment, transfer, and 

 reattachment, molecule by molecule, may be regarded as the initial, 

 and perhaps the most general, phase of metamorphic reconstruction. 

 The process is beautifully illustrated in the granulation of snow at 

 temperatures that inhibit^ liquefaction. It is to be specially noted 

 that this is the work of molecules acting individually. Each offers a 

 special resistance to a special strain, and when freed follows its own 

 path and is drawn into a special new attachment. The action is thus 

 idiomolecular, and is rather sharply distinguishable from isomolecular 

 action, such as takes place in liquid flow. Individual action of this 

 kind makes relatively small demands on the stored energy of strain, 

 but is correspondingly limited and slow in results, and so adequate 

 time becomes a critical matter, but complete reconstruction may be 

 attained in time with lunited strain and limited heat. 



With increase of stress and consequent increase of strain, and also 

 increase of heat, idiomolecular reorganization is hastened. Fur- 

 thermore, it is likely to be concentrated along lines, planes, belts, or 

 parallelisms of some kind. The indi\dduality of action takes on a 

 collective aspect without ceasing to be really individual. This may go 

 so far as to verge toward general and simultaneous action, but close 

 analysis seems to show that it remains idiomolecular in actual method. 

 By such quasi-collective but really idiomolecular action, cleavage, 

 schistosity, and other forms of structural parallelism arise. In gla- 

 ciers it seems to range from the granulation of the snow to the limit 

 of glacial motion.^ 



By further increases of stress, the strain limit may be reached and 

 definite fracture and shear take place. The process then becomes 

 diastrophic rather than metamorphic. 



It has been very commonly held that when depths and pressures 

 are reached that inhibit fracture, general movement of the molecules 

 upon one another after the fashion of liquids takes place. The original 

 idea of "rock-flow" seems to have sprung from this notion. Such a 

 general movement of molecules upon one another, however, especially 

 in a highly rigid body, would require a maximum of differential stress^ 

 for the rigid attachments of all the molecules would have to be 

 disrupted simultaneously. Easement along a few planes, with idio- 

 molecular adjustment between, would require much less energy, and 

 would probably meet all the requirements of the slowly growing 

 stresses of the interior. While the balanced stresses steadily grow 



^C. S. Peet and E. C. Perisho, working with the writer in the winter of 1904, found by daily 

 micrometric measurements that on the average the larger granules grew every day whether 

 the temperature was above or below 0° C. 



^It was from the study of the granu'ation of snow, the growths of glacial granules, and the 

 development of schistosity in the glaciers of Greenland in 1894, that the importance of this indi- 

 vidual action of molecules was realized by Chamberlin and distingmshed from true flow. (Glacial 

 studies in Greenland, Pres. Address, Geol. Soc. Amer., Bull. Geol. Soc. Amer., vol. 6, pp. 209-214, 

 1895.) 



