656 JOSEPH BARRELL 



by Petit in 1849.' Archdeacon Pratt of Calcutta showed a few 

 years later that whereas a discrepanc}^ of 5.2'' existed between the 

 geodetic and astronomic latitudes of Kalianpur and Kaliana, the 

 calculation of the effect of the Himalayas called for a difference of 



These facts were definitely formulated into a theory of isostasy 

 by the Astronomer Royal of Great Britain, G. B. Airy, within a 

 year following the appearance of Pratt's paper,^ though it remained 

 for Button to recognize the large geologic significance and to coin 

 for the relations of elevation and density the word isostasy.'' Fol- 

 lowing this Putnam and Gilbert showed by gravity measurements 

 that a considerable degree of regional isostasy existed over the 

 United States.^ Since then has appeared the much more detailed 

 work of Hayford and Bowie, the computations made by the comput- 

 ing ofi&ce of the United States Coast and Geodetic Survey under 

 their directions making possible this present investigation. 



Thus there has developed through more than half a century 

 evidence beyond controversy which shows that the earth's crust 

 in its larger relief and, within certain limits, even its smaller features, 

 such as the great plateaus and basins, rests more or less approxi- 

 mately in flotational equilibrium. 



The second division of the larger problem of isostasy, that of the 

 areal limits and degree of perfection of isostatic adjustment, is the 

 subject which has been dealt with in the previous parts of this 

 investigation. It has been found that, although the relations of 

 continents and ocean basins show with respect to each other a high 



^ "Sur la latitude de I'Observatoire de Toulouse, la densite moyenne de la Chaine 

 des Pyrenees, et la probabilite qu'il existe un vide sons cette chaine," Comptes rendus 

 de VAcad. des Sc, XXIX (1849), 73°- 



2 "On the Attraction of the Himalaya Mountains and of the Elevated Regions 

 beyond Them, upon the Plumbline in India," Fhil. Trans. Roy. Soc, Vol. CXLV 



(1855). 



3 G. B. Airy, "On the Computation of the Effect of the Attraction of Mountain 

 Masses as Disturbing the Apparent Astronomical Latitude of Stations in Geodetic 

 Surveys," Phil. Trans. Roy. Soc, Vol. CXLV (1855). 



•* "On Some of the Greater Problems of Physical Geology," Bull. Phil. Soc. Wash., 

 XI (1889), 53. 



sBull. Phil. Soc. Wash., XIII (1895), 31-75. 



