GEOLOGY — CHAMBERLIN. 1 79 



take the form of sheets or lenses intervvedged among the foliations, 

 particularly those that were more nearly horizontal. These intrusions 

 may be assumed to have tended to take two forms — the first distribu- 

 tive, consisting of an intimate intrusion of thin sheets between the 

 folise of the sheared zone, and the other more concentrative, in the 

 form of large lenses, with, of course, irregularities of all sorts. 



» 2) It is conceived that the shear zone of the earliest ages has been 

 exposed by denudation where the bod}- of the earth was most protuber- 

 ant, and that this exposed portion constitutes at least a part of the 

 great foliated and schistose area of the Archean, with its abounding 

 and extensive batholiths. Thus the extraordinary prevalence of folia- 

 tion and schistosity, with interleaved igneous layers and embedded 

 batholiths, finds a seemingly consistent explanation. The shearing 

 itself may tax our dynamical conceptions, but if it is required by the 

 phenomena of folding there is some dynamic gain in finding in it also 

 a solution of the rather grave problems presented by the prevalent 

 foliation and the prodigious batholiths of the Archean. The forma- 

 tion of the foliation by the mashing of a relatively thick crust and the 

 introduction of the batholiths by the massive vertical intrusion of 

 great igneous bodies make very severe demands on dynamical energies. 



By the foregoing combination of deep-seated and superficial agen- 

 cies the different grades of deformations of the primary order are 

 thought to be consistently accounted for, both in the matter of pro- 

 viding for an adequate amount of shrinkage and in its proportional 

 application to the different classes of deformations. More specifically , 

 it is thought that in the rearrangement of heterogeneous material in 

 the body of the earth, combined with internal transfers of heat as 

 well as external loss, together with volcanic extrusions, adequate 

 possibilities of shrinkage are postulated, even when it is recognized 

 that this shrinkage must have been large. A similar adequacy can 

 not apparently be assumed with equal confidence when external loss 

 of heat, vulcanism, and other superficial changes, of whatever kind, 

 are alone appealed to. In the differential shrinkage of the great 

 sectors under the modifying action of the atmosphere and hydro- 

 sphere during growth, an apparently competent agency for the 

 development of continental platforms and oceanic basins is provided. 

 In the differential shrinkage of deep segments of the outer portion 

 of the earth is postulated a seemingly adequate and appropriate 

 agency for the formation of plateau-like protuberances and the great 

 differential swells of the continental protuberances, while in the shear 

 of a very superficial shell whose rigidity is too high relative to its 

 weighting to be plastically deformed is found the agency involved in 

 the foldingof mountain ranges and the phenomena of overthrust faults. 



