SECTIONAL TRANSACTIONS.— C. 365 



instiumeriis employed should be placed in excavations and protected from dis- 

 turbing influences. They should be located in plains with uniform geological 

 structure and surface character. 



(b) Prof. H. H. Turner, F.R.S. — The Astronomical Evidence 

 Bearing upon the Hypothesis. 



The only piece of astronomical evidence supporting Wegener's hypothesis, 

 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 correspondence, both 

 stratigraphical and palasontological, from the Pre-Cambrian up to the Creta- 

 ceous, and in particular brings to light certain facts even more strikingly 

 indicative of a former rapprochement between the two continents than any 

 pointed out by Wegener. 



The recurrence in America, on opposite sides of the old Appalachia, of the 

 two facies of the Eui'opean Cambrian and early Ordovician, which are here 

 separated by the Caledonian chain, is perhaps the most striking, the lithological 

 and faunal distinctions and the sequences of transgression and recession, 

 different on either side of the chain, being reproduced with remarkable pre 

 cision. Again, the continental and marine facies of the Devonian are separated 

 in both countries by boundaries which become conterminous on the Wegener 

 reconstruction. 



The equivalent line in the Triassic lies further south both in Europe and 

 America, but, as it passes into the areas of generally defective correspondence 

 in Spain and Central America, is less valuable as a criterion. It should, on 

 the other hand, be noted that in America there are in the middle of the 

 Carboniferous and Cretaceous formations marked unconformities which have 

 not been recorded in Europe. The investigation of these discrepancies, perhaps 

 more apparent than real, might well form a test case for the theory. 



9. Dr. Herbert L. Hawkins. — The Relation of the River Thames 

 to the London Basin. 



(i) The London Basin is an asymmetrical syncline pitching eastwards. The 

 southern rim dips sharply, the northern gently, the axis lying nearer the south. 

 Drainage of such a district would consist normally of a main stream along the 

 axis with tril)utaries on both sides. This condition is realised in the west 

 by the Kennet and in the east by the Thames below Chertsey. In the inter- 

 vening portion (Theale to Chertsey) the main stream is north of the 'ideal' 

 position, and its southern tributaries cross the axis and flow against the dip 

 At Wargrave the Thames returns into the Chilterns in apparent defiance of 

 all rules and reason. There is evidence that the southern tributaries have 

 postponed junction with the main stream fairly recently, and that the Thames 

 itself has shifted its course southwards. 



The original drainage of tlie basin is believed to have passed along the 

 Kennet to Theale, thence to Pangbourne, along the present Thames to Windsor, 

 thence by Rickniansworth and Hertford, and probably down the Lea. (PoiNsibly 

 it reached the sea past ^laldon or Colchester.) These broad meanders were 

 reversible with similar amplitude. This line was probably the synclinal axis 

 in Miocene and Pliocene times, its southward displacement being due to the 

 increased plunge of the ' North Downs ' dip. Many anomalies in the drainage 

 and river deposits are explicable on this liypothesis, the rivers being incom- 

 pletely adapted to the tectonic change. 



(ii) The Upper Thames is a tributary of the London Basin drainage. New 

 sections in Gorine Gap show that torrent action has deepened the gorge by 

 about fifty feet. Excavations on the hills above Whitchurch afford presumptive 

 evidence of the marginal effects of true glaciation. The nature and arrangement 



