556 Reports & Proceedings — British Association. 



Greenland is moving in the same direction at a still more rapid rate. 

 The continents are composed largely of rocks rich in silica and 

 alumina, " Sial/' while those below the sea are less siliceous and 

 heavier, and have been referred to as " Sima ". This extends under 

 the Sial of the continents at a depth which Wegener estimates at 

 57 miles, which is probably far too great. He believes that the Sial 

 masses drift through the Sima, like icebergs through the sea. The 

 Sima is probably, however, a crystalline solid down to a depth of 

 about 15 miles, and is as strong as, if not stronger than, the Sial. 



By overthrusts and crumpling some areas are brought nearer 

 together, and by Assuring, igneous intrusions, and normal faulting 

 others are moving apart. There is some evidence of a slow drift 

 away from Africa and towards the Pacific, but there is nothing to 

 show that this has been as rapid as is assumed by Dr. Wegener. 

 The Atlantic may have come into existence since Carboniferous times, 

 but this would not mean a separation equal to its whole width, as 

 part of the submergence would be caused by faulting down towards 

 a region of tension. 



The Astronomer-Eoyal of Scotland has shown that determinations 

 of longitude by telegraphy are subject to serious errors. Light is 

 thrown on this by the observations of Hecker and others with 

 horizontal pendulums. In addition to the movements caused by the 

 variations of direction and amount of gravity due to the sun and 

 moon, there are others of greater amplitude, due to diurnal tilting 

 as the result of solar radiation. Similar seasonal effects must also 

 occur. Variations of the barometer in adjoining areas, and of the 

 underground water-level and marine tides, must also affect the 

 pendulums. Most of these effects are considerably less at some 

 depth below the surface, and it is suggested that the instruments 

 employed should be placed in excavations and protected from 

 disturbing influences. They should be located in plains with 

 uniform geological structure and sm-face character. 



(6) Professor H. H. Turner, F.K.S. — The Astronomical Evidence 

 bearing upon the Hypothesis. 



The only piece of astronomical evidence supporting Wegener's 

 h^'-pothesis, and worthy of serious consideration, is the apparent drift 

 of Greenland. The observations in 1870 and 1907 show a change 

 of 1,200 metres, and observations in 1823 lend some support, but 

 it cannot be said that the drift is established beyond doubt, though a 

 good case is made for repeating the observations to-day ; indeed, 

 the matter is so important that this is a duty. All the other evidence 

 is practically against such changes in modern times. 



(c) Mr. W. B. Wright. 



A critical comparison of the geological formations on the two sides 

 of the North Atlantic shows on the whole a very remarkable corre- 

 spondence, both stratigraphical and palaeontological, from the 

 Pre-Gambrian up to the Cretaceous, and in particular brings to light 



