564: Notices of Memoirs — Dr. Mackie^- Continents 8f Ocean Basins,. 



11. — A Theory of the Origin of Continents and Ocean Basins^ 

 By William Mackie, M.A., M.D.^ 



WHATEVER the conditions at present obtaining in the interior 

 of the earth, it is naturally supposed to have originally passed 

 through a stage which would be represented by a solid, or potentially 

 solid, nucleus, a slowly forming and slowly thickening acid crust, 

 with a liquid and more or less basic interstratura. At first the crust 

 would be sufficiently flexible to accommodate itself to the tidal 

 movements of the subjacent liquid interstratum, but when it became 

 too rigid to admit of this tidal movement it would be broken up, 

 the fracture probably following certain fairly defined and assignable 

 lines. It is argued that the fragments would not have ' gone under,' 

 but would have remained with their surfaces at a considerably higher 

 level than the surface of the magma, and have become so fixed by 

 consolidation of the magma around them. 



It is suggested that the first great breach in the crust followed 

 the outline of the tidal protuberance, and was, in all probability,, 

 effected at some conjunction of the sun and moon with cataclysmal 

 suddenness, the intervening crust being shivered into small frag- 

 ments, these fragments being subsequently disposed of by fusion in, 

 and incorporation with the magma. The first oval breach thus 

 caused is the prototype of the Pacific Ocean. Further fractures, it 

 is suggested, gave rise to the other oceans, and caused the separation 

 of the continents. Under the influence of tidal retardation the 

 fragments as thus blocked out became separated and finally moored 

 at their respective distances by the solidification of the magma 

 around them. 



With the resolidification of the crust, a series of stresses was set 

 up between the ocean basins, which consisted of the more basic, con- 

 sequently specifically heavier, more quickly conducting material, and 

 the more acid, specifically lighter, more slowly conducting con- 

 tinental masses. The former are, in consequence of their character 

 and composition, the more stable portions of the resolidified crust. 

 Further cooling therefore leads to their sinking down on the cooling 

 and shrinking nucleus, and their elbowing aside of the continental 

 masses, which come to be elevated in lines parallel to and extending 

 along their margins. With further cooling the superficial layers of 

 the continents are thrown into folds and overfolds, which would 

 tend to find relief along the ocean margins by thrusts directed from 

 the continents towards the oceans. Central uplifts in the continental 

 areas also may have resulted from such pressure. 



The tendency of the ocean to become deeper and the continent ta 

 become more elevated as time goes on, leads more and more to the 

 withdrawal of the waters of the ocean (which might at first almost 

 or altogether have covered the continental areas) from these areas, 

 and hence to greater and greater restriction in the limits of the areas 

 of deposit as traced from earlier to later geological times. 



^ Abstract of paper read before the British Association, Southport, Section C 

 (Geology), September, 1903. 



