lis NATURAL SCIENCE [February 



ocean currents, and the formation of a fresh outlet through the 

 Straits of Dover. 



The first geologist to realise the full geological significance of the 

 inconstancy of the sea level was Professor Eduard Suess, of Vienna. 

 Eecognising the importance of this fact he set to work to enquire 

 if it could yield any help in developing a theory of geographical 

 evolution. Geographers have always agreed that the distribution of 

 land and water on the earth is not a haphazard arrangement, but is 

 governed by some principle or law. There is, it is true, a remark- 

 able dissimilarity between the different continents ; but a closer 

 comparison reveals many striking repetitions of the same arrange- 

 ment. At first sight no two structures could look less alike than 

 a quartz crystal, with its solid form and its simple outline, its flat 

 faces and its straight edges, and a complex crystalline flake of 

 snow, with its radiating cluster of feathery tufts of delicate filigree. 

 But the crystallographer recognises that the quartz crystal and 

 the snow flake have the same simple hexagonal symmetry, and are 

 built on the same fundamental plan. So the geographers have felt 

 that if we neglect accidental topographical details, we find so many 

 points of striking resemblance between the great land masses, that 

 there must be some underlying symmetry in continental form. A 

 convincing statement of these coincidences was made by Professor 

 Lap worth in a lecture to the Geographical Society in 1894, and 

 formed the text of his presidential address to the Geological Section 

 of the British Association at Edinburgh in 1892. 



Quite early in the century, geologists set to work to construct 

 theories that would explain continental forms, but with little suc- 

 cess. The well-known southward direction of all peninsulas was 

 stated in elementary text-books of geography, and was often ex- 

 plained as due to the southern hemisphere having a larger share 

 of the ocean than its due, owing to its being heavier than the 

 northern hemisphere. Several efforts have been made to attri- 

 bute the direction of the main mountain chains to lines of weakness 

 by torsion in the original crust of the earth. The theory is still 

 popular, in spite of the overwhelming weight of palaeontological 

 evidence against it, that the ocean basins and the continental 

 masses were determined in the pre-zoic period, and that they 

 have been permanent throughout geological time. These theories 

 of continental form have, however, been either so vague as to be 

 useless, or if sufficiently definite to be helpful, they have been 

 shewn inconsistent with essential facts. 



As M. Bertrand shows in an admirable preface to the French 

 translation, Elie de Beaumont's brilliant speculations failed owing 

 to his having filled the gaps in his foundation of facts by guesswork. 

 Suess realises this danger, and accordingly sets to work on a different 



