﻿viii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. lxxii, 



The following communication was read : — 



'The Physical Geograplry of Bournemouth.' By Henry Bury, 

 M,A., F.L.S., F.G.S. 



Lantern-slides and an enlarged sketch-map were exhibited by 

 the Author in illustration of the above paper. 



February 2nd, 1916. 



Dr. A. Smith Woodward, F.R.S., President, 

 in the Chair. 



Arthur W. Dean. B.Sc, 111 Winston Road, Stoke Newington, N., 

 was elected a Fellow of the Society. 



The List of Donations to the Library was read. 



A Lecture was delivered by Richard Dixon Oldham, F.R.S., 

 on the Support of the Himalaya. 



He said that it was known that the major prominences of the 

 Earth's surface are in some way compensated by a defect of density 

 underlying them, with the result that they do not exert the 

 attractive force, either in a vertical or in a horizontal direction, 

 which should result from their mass. A study of the distribution 

 of this compensation shows that there is a general balance between 

 it and the topography, such that the weight of any vertical column 

 through the crust of the earth is, on the average, constant, what- 

 ever may be the elevation of the surface. To this condition the 

 term isostasy has been applied, which does not merely denote a 

 static condition, but implies a power of adjustment of the com- 

 pensation to the variation in load produced by surface-denudation 

 and transport. 



The explanations that have been proposed of the existence of 

 compensation fall into two classes. One supposes the relief of the 

 surface to be due to an alteration in the volume of the underlying 

 rock, and may be regarded as hypotheses of tumefaction. 

 They involve no addition of matter to the crust under a mountain- 

 range, and do not provide, either for any departure from a balance 

 between topography and compensation, or for a restoration of the 

 balance when disturbed by denudation. The other group of 

 hypotheses attributes the origin of the range to a compression of 

 the crust, the injection of molten matter, or the 'undertoAV ' of the 

 lower part of the crust. To provide for compensation, any hypo- 

 thesis of this class will require a downward protuberance of the 

 nether surface of the crust, causing a displacement of denser by 

 lighter material, as also an effect of buoyancy owing to this 



