110 ROCK-METAMORPHISM. 



is divisible into two sections east-of -north, and west-of-north ; 

 a third section, not so strongly developed, remains to be 

 added, which, running north and south (that is, between the 

 others), may be called medio-meridional. The equatorial 

 system, in general not so well developed, may also be divided 

 into two or more sections. As the earth's continents and 

 great peninsulas (India &c.) have their chief coast-lines run- 

 ning in directions corresponding to the two principal meridional 

 sections (which is also the case with the main trends of the 

 islands of the Pacific and other oceans), my contention is that 

 their east coast-line belongs to, and has been aligned by, the 

 east-of-north meridional jointing also that their west coast-line 

 stands in corresponding relation to the west-of-north section. 

 Thus I look upon the coast-lines of continents as a correlated 

 phenomenon, taking these features to be defined by the edges of 

 the great submarine plateaux which, stretching out for 200 miles 

 or more, abruptly terminate in a succession of bench-like 

 terraces, suddenly descending into the abysses of the oceans. 



Respecting another prominent feature of our continents, I offer 

 the suggestion that the east-of-north and the west-of-north sec- 

 tions of meridional jointing have primarily marked out the sides 

 of the triangle under the form of which these great land-masses 

 are for the most part presented ; while the base of the triangle 

 is ascribed to equatorial jointing. But as it is not yet clear to me 

 why the base of the triangle faces the north and its apex points 

 to the south, I am inclined to think the solution lies in the fact 

 that the greatest elevated land-masses characterize the northern 

 hemisphere and equatorial regions a disposition which would 

 cause a greater width of elevated land to lie within the basal area 

 of the triangle than at the apex. 



This last point requires to be considered in connexion with 

 the theory originally advanced by Dana"*, that the earth's con- 

 tinents have always been continents, or, as I prefer to put it, 

 that the present continents, in the main, have been from the 

 earliest geological periods greatly elevated regions separated by 

 enormously deep depressions. Dana, however, contends that 

 the great land-features of the globe have been produced by 

 regional up-bendings and down-bendings of its crust, the 

 former having given rise to continental masses, and the latter 

 to vast ocean-basins ; whereas, although accepting the pre- 

 * { American Journal of Science/ 1846, and ' Manual of Geology.' 



