48 MIDDLEMISS: THE GEOLOGY OF IDAE STATE, 



magma reservoirs at unknowable depths is responsible for nil the 

 varieties of igneous rocks, does not seem to stand the strain of 

 modern arguments as exemplified in recent penological and geo- 

 physical writings, such as Daly's elaborate treatise {he. cil.) and 

 the concise but extreme form of the same ideas by Stanislas Member. 1 

 The researches of H. Jeffreys 8 on the viscosity of the earth, which 

 have led him to conclude that the earth as a whole is plastic, 

 and that the lithosphere has the hydrostatic form to a high degree 

 of accuracy, must also seriously influence our conceptions of the 

 physical conditions underground at great depths, and of the amount 

 of molar and molecular readjustments (deformations) that must be 

 continuously at work with their accompanying dynamic metamor- 

 phism. 



Before closing this account of the calc-gneisses and other asso- 

 ciated rocks, it is necessary to remark on the 



from certain narrow and straight bands m 

 the railway cutting near Khed Brahma (see p. 18). These show a 

 series of stages in the progress of mylonitisation of the calcite 

 ground-mass. Effects of this kind have frequently been noticed in 

 crystalline limestones, and were long ago adduced as evidence of 

 dynamic stresses acting on the rock since solidification. 3 Such 

 destructive cataclastic effects, however, are now generally inter- 

 preted as belonging to a comparatively recent crushing which has 

 taken effect locally near the present surface of the ground in 

 the ' zone of fracture,' as contrasted with the more general deep- 

 seated phenomena we have been considering in the ' zone of flow " : 

 where plastic deformation, embodying crushing with recrvstallisa- 

 tion and foliation (constructive dynamic action) has resulted in a 

 widely different order of effects. The former are rare in the crystal- 

 line rocks of this part of India, the latter are universal in the 

 Archeean, and, though showing no crystal fracture now. may none 

 the less imply a far intenser phase of dynamic metamorphism. 



Here we must leave the problem for the present until other 

 facts in neighbouring areas of what may be related rocks, have 

 received due attention. 



i Proc. Acad. Nat. 8c, Philadelphia, Vol. LXVII, pt. 2, p. 351, (1915). 

 z Mem., Roy Astr. Soc, Vols. LX, LXXV and LXXVI (1915) as reviewed in the 

 Geological' Magazine for March, 191(i, by A. Holmes. 



a Geological Structure of the N- W. Highlands, 1907, p. 598. 



