October 16, 1914] 



SCIENCE 



541 



that the injection of large bodies of basic 

 material into the shell of tension tends on 

 purely mechanical grounds to the forma- 

 tion of a depression, or geosyncline. If 

 this be so, are we justified in assuming that 

 the heavy band following the southern 

 margin of the Gangetic geosyncline is a 

 "range" of such batholiths? The idea is 

 not entirely new; for 0. Fisher made the 

 suggestion more than twenty years ago that 

 the abnormal gravity at Kalianpur was 

 due to "some peculiar influence (perhaps 

 of a volcanic neck of basalt )."^° 



Daly's suggestion, however, taken into 

 account with the history of Gondwanaland, 

 may explain the peculiar alignment of the 

 heavy subterranean band, parallel to the 

 Gangetic depression and parallel to the 

 general trend of the peninsular tension- 

 faults and fissures that followed the un- 

 loading of Gondwanaland and the heavy 

 loading of the adjoining ocean bed along a 

 band roughly parallel to the present Hima- 

 layan folds. 



R. S. Woodward objected that isostasy 

 does not seem to meet the requirements of 

 geological continuity, for it tends rapidly 

 towards stable equilibrium, and the crust 

 ought therefore to reach a stage of repose 

 early in geologic time.^° If the process of 

 denudation and rise, with adjoining de- 

 position and subsidence, occurred on a solid 

 globe, this objection might hold good. But 

 it seems to me that the break-up of Gond- 

 wanaland and the tectonic revolutions that 

 followed show how isostasy can defeat it- 

 self in the presence of a sub-crustal magma 

 actually molten or ready to liquefy on local 

 relief of pressure. It is possible that the 



19 "Physics of the Earth's Crust," 2d ed., 

 1889, p. 216. 



20 ' ' Address to the Sect, of Mathematics and 

 Astronomy of the Amer. Assoc," 1889, Smifli- 

 sonian Report, 1890, p. 196. 



protracted filing off of Gondwanaland 

 brought nearer the surface what was once 

 the local level of no-strain and its accom- 

 panying shell of tension. 



The conditions existing in northern 

 Gondwanaland before late Mesozoie times 

 must have been similar to those in south- 

 west Scotland before the occurrence of the 

 Tertiary eruptions, for the crust in this 

 region was also torn by stresses in the 

 S.W.-N.B. direction with the formation of 

 a remarkable series of N.W.-S.E. dykes 

 which give the one-inch geological maps in 

 this region a regularly striped appearance. 



There is no section of the earth's sur- 

 face which one can point to as being now 

 subjected to exactly the same kind and 

 magnitude of treatment as that to which 

 Gondwanaland was exposed for long ages 

 before the outburst of the Deecan Trap; 

 but possibly the erosion of the Brazilian 

 highlands and the deposition of the silt 

 carried down by the Amazon, with its 

 southern tributaries, and by the more east- 

 ern Araguay and Tocantins, may result in 

 similar stresses which, if continued, will 

 develop strains, and open the way for the 

 subjacent magma to approach the surface 

 or even to become extravasated, adding 

 another to the small family of so-called 

 fissure-eruptions. 



The value of a generalization can be 

 tested best by its reliability as a basis for 

 prediction. Nothing shows up the short- 

 comings of our knowledge about the state 

 of affairs below the superficial crust so 

 effectually as our inability to make any 

 useful predictions about earthquakes or 

 volcanic eruptions. For many years to 

 come in this department of science the only 

 worker who will ever establish a claim to 

 be called a prophet will be one in Cicero's 

 sense — "he who guesses well." 



Thomas H. Holland 



