276 THE POORNESS OF OUR Chap. IX. 



rich fossiliferous formation, thick cnougli, \\hvn upraised, to 

 resist a large amount of denudation, may be formed. 



I am convinced that nearly all our ancient formations, which 

 are throughout the greater part of their thickness rlcJi in fos- 

 sils, have thus been formed during subsidence. Since publish- 

 ing my views on this subject in 1845, 1 have watched the prog- 

 ress of Geology, and have been surprised to note how author 

 after author, in treating of this or that great formation, has 

 come to the conclusion that it was accumulated during. sub- 

 sidence. I may add 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 deposit- 

 ed during a downward oscillation of level, and thus gained 

 considerable thickness. 



All geological facts toll us plainly that each area has under- 

 gone numerous slow oscillations of level, atid apparently these 

 oscillations have affected Avide spaces. Consequently forma- 

 tions rich in fossils and sufficiently thick and extensive to re- 

 sist subsequent degradation, may have been formed over wide 

 spaces during periods of subsidence, but only where the sup- 

 ply of sechment was sufficient to keep the sea shallow and to 

 embed and preserve the remains before they had time to deca3% 

 On the other hand, as long as the bed of the sea remained sta- 

 tionary, thich deposits could not hare been accumulated in the 

 shallow parts, which are the most favorable to life. Still less 

 could this have happened during the alternate periods of ele- 

 vation ; or, to speak more accurately, the beds which were 

 then accumulated Avill generally have been destroyed by being 

 upraised and brought within the limits of the coast-action. 



These remarks appl}'" chiefly to littoral and sub-littoral de- 

 jiosits. In the case of an extensive and shallow sea, such as 

 that within a large part of the Malay Archipelago, Avhere the 

 depth varies from 30 or 40 to 60 fathoms, widely-extended for- 

 mation might be formed during a jicriod of elevation, and yet 

 not suffer excessively fr©m denudation during its slow up- 

 heaval ; but the thickness of the formation could not be great, 

 for owing to the elevatory movement it would be less than the 

 depth in whidi it was formed ; nor would the deposits be much 

 consolidated, nor be cajiped by ovcrlj-ing formations, so that 

 it would run a good chance of being worn away by atmos- 

 ])heric dc^gradation and by the action of the sea during subse- 

 quent oscillations of level. It has, however, been suggested 



