part 2] PROCEEDINGS OF THE GEOLOGICAL SOCIETY. cvii 



May 2nd, 1923. 



Prof. A. C. Seward, Sc.D., F.E.S., President, 

 in the Chair. 



Frank Higham, B.Sc., A.R.S.M., 57 Widdrington Road, 

 Coventry ; and Marie Vobe, Roselea, Abbey Wood Poacl, Abbey 

 Wood, S.E. 2, were elected Fellows of the Society. 



The List of Donations to the Library was read. 



Prof. John Jolt, D.Sc, F.P.S., F.G-.S., then proceeded to deliver 

 a lecture on the Bearing of some Recent Advances in 

 Physical Science on Geology. 



After referring to the discovery by the present Lord Payleigh 

 of the general distribution of radioactive materials and to the 

 earlier but more recently developed discovery of isostasy, the 

 Lecturer observed that, assuming that the dense layer upon which, 

 according to the theory of isostasy, the continents iloat, is com- 

 posed of basalt possessing the average radioactivity of basalts, it 

 ma.j be calculated that, if this substratum is now solid (as 

 appears from both tidal and seismological evidence), it will have 

 acquired sufficient radioactive heat to become fluid in about 

 30 million years. 



The change of density then occurring will cause a downward 

 motion of the continents relative to the ocean, and transgressional 

 seas will result. After a long period, during which the licraid 

 magma (under tidal forces) circulates from beneath the continents 

 (which, owing to their own radioactivity, act as an adiatherminous 

 covering) to suboceanic regions, the accumulated heat is given up 

 to the ocean. Re-solidification of the magma ensues, and the 

 restoration of the former higher density causes the continents to 

 rise relatively to the oceans, and brings about the retreat of 

 transgressional seas. In this manner, the complete cycle of a 

 revolution finds explanation. 



Mountain-building forces arising during the climax of revolution 

 originate from two sources: — (a) the effects of the horizontal 

 tide-generating force and of precessional force which, although 

 probably considerable, have not yet been evaluated ; (b) the effects 

 of the changing area of the ocean-floor attending the expansion 

 and contraction of the basaltic layer, whereby the oceanic area 

 becomes alternately increased and diminished. Upon shrinkage 

 the enlarged ocean-floor bears against the continents. Hence 

 'the highest mountains confront the widest oceans'. 



Mountain-building is due much more to vertical than to hori- 

 zontal forces. The mountains are not pushed up by lateral forces : 

 these forces act upon the subsiding geosyncline to produce deform- 

 ation of the semi-plastic materials. The mountains are elevated 



