I92I. No. II. THE STR.\.\DFLAT AND ISOSTASY. 29I 



upjKT Strata uf the crust would Ijc raised, iu Spitsbergen even as much 

 as about ten degrees centigrade, and not lowered if the land were covered 

 ])y a thick ice-sheet. 



As to the second theory, it is in itself inconceivable that tangential 

 pressure of any kind should be able to produce an upheaval so regular and 

 so gradual over an area as extensive as Fenno-Scandia, especiallv con- 

 sidering the comparatively narrow ridges produced by mountain-folding. 

 A conclusive proof against tliis theory, however, is given by the strandfiat, 

 showing that the crust has first been pressed down in late-glacial time, 

 and has then again ])een raised to its original level. A tangential pressure 

 or strain causing such regular vertical movements of the crust is not 

 conceivable. 



Penck's theory has been disproved b^ Hergesell [18871, Drvgalski 

 [1887', ^^'codward [1888;. and de Geer [1888] and was abandoned by 

 Penck himself. The fact that the rise of sea-level caused by the attraction 

 of the ice-masses would cease the moment the ice retreated, while the 

 upheaval of the land occurred long after that time, is in itself conclusive 

 proof against this theory. 



It seems to me that the more one studies the whole process of the 

 late-glacial and postglacial subsidence and upheaval of Fenno-Scandia, and 

 the related crustal movements in the surrounding regions, in all their 

 details, the more one must l)e convinced that these movements are iso- 

 static. One will finrl that the theory of isostasy gives a simple and natural 

 explanation of almost all phenomena, and even of manv details which mav 

 seem startling at the first glance. 



The Theory of Isostasy. 



It seems strange that although the idea of isostasy is now more than 

 seventy years old in literature, and in spite of all that has been written 

 about it, the views regarding it still differ widelv, especiallv amongst 

 geologists. 



Elie de Beaumont suggested already in 1848 that accumulation 

 of load depresses the disks of the crust, and removal of load will cause 

 their upheaval. Some years later Pratt [1855 and 1859] and Airv [1855] 

 clearly propounded the theory of the isostasy of the lithosphère. The name 

 isostasy was, however, introduced much later by C. E. Dutton [1892]. 

 A long series of prominent geophysicists have further developed the theory 

 of isostasy, and the correctness of Airy's view^s seems to have been sup- 

 ported by numerous observations. 



Airy's theory was based on Archdeacon Pratt's determinations of 

 the deflection of the plumb line in India, showing that the attraction of 

 the Himalaya mountains was less than might be expected to be exerted 



