256 THE POORNESS OF OUR [CHAP. X. 



that the only ancient tertiary formation on the west coast of 

 South America, which has been bulky enough to resist such 

 degradation as it has as yet suffered, but which will hardly last 

 to a distant geological age, was deposited during a downward 

 oscillation of level, and thus gained considerable thickness. 



All geological facts tell us plainly that each area has undergone 

 numerous slow oscillations of level, and apparently these oscilla- 

 tions have affected wide spaces. Consequently, formations rich 

 in fossils and sufficiently thick and extensive to resist subsequent 

 degradation, will have been formed over wide spaces during 

 periods of subsidence, but only where the supply of sediment was 

 sufficient to keep the sea shallow and to embed and preserve the 

 remains before they had time to decay. On the other hand, as 

 long as the bed of the sea remains stationary, thick deposits 

 cannot have been accumulated in the shallow parts, which are 

 the most favourable to life. Still less can this have happened 

 during the alternate periods of elevation ; or, to speak more 

 accurately, the beds which were then accumulated will generally 

 have been destroyed by being upraised and brought within the 

 limits of the coast-action. 



These remarks apply chiefly to littoral and sub-littoral deposits. 

 In the case of an extensive and shallow sea, such as that within 

 a large part of the Malay Archipelago, where the depth varies 

 from 30 or 40 to 60 fathoms, a widely extended formation might 

 be formed during a period of elevation, and yet not suffer exces- 

 sively from denudation during its slow upheaval ; but the thick- 

 ness of the formation could not be great, for owing to the elevatory 

 movement it would be less than the depth in which it was formed ; 

 nor would the deposit be much consolidated, nor be capped by 

 overlying formations, so that it would run a good chance of being 

 worn away by atmospheric degradation and by the action of the 

 sea during subsequent oscillations of level. It has, however, been 

 suggested by Mr. Hopkins, that if one part of the area, after 

 rising and before being denuded, subsided, the deposit formed 

 during the rising movement, though not thick, might afterwards 

 become protected by fresh accumulations, and thus be preserved 

 for a long period. 



Mr. Hopkins also expresses his belief that sedimentary beds of 

 considerable horizontal extent have rarely been completely de- 

 stroyed. But all geologists, excepting the few who believe that 

 our present inetamorphic schists and plutonic rocks once formed 

 the primordial nucleus of the globe, will admit that these latter 

 rocks have been stript of their covering to an enormous extent. 

 For it is scarcely possible that such rocks could have been solidified 

 and crystallized whilst uncovered ; but if the metamorphic action 

 occurred at profound depths of the ocean, the former protecting 



