Groundwork for Study of Megadiastrophism. 255 



The prime function of the method is to disclose the actual 

 zones of weakness, or at least zones of yield, that is, one 

 type of asthenozones. Though the matter dealt with was 

 solid, it was not "perfect solidity" in the sense implied 

 by the reviewer's statement. Obviously, as the diagrams 

 and text of the original papers abundantly show, it was a 

 yielding solidity. In its application to the Appalachians 

 of Pennsylvania and the Colorado Rockies, the method 

 disclosed plunging zones of yield, but at the same time the 

 masses enclosed within these yield tracts showed the same 

 sort of deformation that had usually been assigned them 

 by advocates of a molten earth. The wedge-body did not 

 show ' k absolute rigidity" or imply the ''non-existence 

 of a yield-state" "for almost any condition of stress" 

 (p. 396). The plunging zones of yield are supplemental 

 asthenic zones, and add just so much of detectable yield 

 to what was known from the accessible deformations 

 above. Thus, far from being inhibitory of horizontal 

 yield — the assigned function of the asthenosphere — the 

 plunging yield-zones do good service by revealing the 

 mode by which horizontal yield actually took place in 

 these particular cases. 



The reed ciuestion of an asthenosphere in the earth as it 

 actually is. — Our critic's definition of the asthenosphere 

 as a zone at no great depth "which yields to diastrophic 

 differential stresses" is so broad as to include any view 

 that accepts general internal deformation. Under the 

 new view of the constitution of matter, it seems clear that 

 all zones yield to diastrophic differential stresses. The 

 real question is whether there is a zone at no great depth 

 below the surface which yields in a special degree com- 

 pared with the zones above and below. 



The doctrine of an asthenosphere as set forth by its 

 author, Dr. Joseph Barrell, was made to relate mainly to 

 a solid elastico-rigid zone, as will be seen by reference to 

 the original papers. 2 He assigned a mode of movement 



- J. Barrell, ■ ' The Strength of the Earth 's Crust. ' ' Part VI. Kelations of 

 Isostatie Movements to a Sphere of Weakness — the Astlrenosphere : Part 

 VII. Variations of Strength with Depth as Shown by the Xatnre of Depar- 

 - from Isostasy. See. A. Presentation of Theory. Sec. B. Applica- 

 tions of the Theory: Part VIII. Physical Conditions Controlling the 

 Nature of Lithosphere ami Asthenosphere. Sec. A. Belations between 

 Eighlity, Strength, and Igneous Activity. Sec. B. Belations with other 

 Fields of Geophvsics. Jour. Geol., vol. 22, pp. 655-'-:;. 729-41. 1914. vol. 

 23, pp. 27-44, 425-32, 499-515, 1915. 



