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era hemisphere, containing in the ascending order, first, beds 

 with organic remains belonging to the south temperate zone ; 

 another series of beds inclosing marine and terrestrial ani- 

 mals corresponding to those of the tropics resting on them ; 

 and again, beds of marine and freshwater shells alternating, 

 similar to those now living in the northern hemisphere, com- 

 pleting the series : such a formation would show that the beds 

 must have undergone a considerable oscillation since the com- 

 mencement of their deposition. The whole series, in moving 

 from zone to zone, would be governed by the local nature of the 

 base on which it rested, and would necessarily conform to all 

 the changes which may periodically occur in the inferior bed. 

 One of the most satisfactory results arrived at in the study of 

 the sedimentary rocks, is the certainty that the subterranean 

 movements of the solid crust of the globe, to which the deranged 

 positions of the strata are owing, were not all of the same date, 

 but that some mountain ridges and some lines and points of 

 stratified rocks had been bent and disturbed before others were 

 formed. 



Let us suppose a coal formation to be now forming near the 

 mouth of the Rio de la Plata, and the movement en masse 

 northward to be 20 seconds per annum, it would take 2200 

 years to arrive within the tropic of Capricorn; during this 

 period there would be very considerable changes in the confi- 

 guration of the land ; and when we consider the longitudinal ex- 

 tent of the movement, say about 750 miles, we need not be sur- 

 prised that the mass should happen to be much contorted and 

 elevated or depressed a few thousand feet from its former rela- 

 tive position. From the tropic of Capricorn to the equator the 

 sedimentary mass may remain above the level of the sea and 

 form the habitation of the organic beings confined to that 

 part of the earth, whilst another mass of the same age may still 

 remain under water. From the equator to the tropic of Cancer 

 it may become again submerged below the level of the sea, 

 and thus receive additional layers of sedimentary beds ; on its 

 emergence from the sea in the northern hemisphere, it would 

 present an undulated compound, containing a different series of 

 organic remains belonging to distinct zones, with one strong 

 line of demarcation, showing the absence of the beds belonging 



