314 ORIGIN OF SPECIES 



age, was deposited during a c?.*:i.-ird cscfZsr:!?:: of 

 and ditts gained ctmsiderakie thirkness. 



An geologica] facts tell ns plaiohr that each 3.rt3. -3^ under- 

 gone nameroas 5lo"w osciilations of level, and ^.r^Mrentlv these 

 oscillaticHis bave asected wide spaces. Coaisectienthr, foraaft- 

 tions rich in fossils and sofBaently thick and extensile to 

 resist snhsequient degradaticm, will have been :£cKined otO" 

 wule spaces dnring periods ci subsidence, bet only wirere tiie 

 supply of sediment was sufficient to keep the sea sbaDow and 

 to embed and preserve the resnains before tfaey had time to 

 decay. On die other hand, as l(Xig as the bed of the sea 

 remains stationary, tkick deports cannot have been accnoni- 

 tated in the shallow parts, which are the most favoarafaie to 

 Hfe. Still less can this have ha£^>ened cfaning the ahemate 

 periods of elevation: or, to speak more accnratdy, tfse be<^ 

 which "w^re then acctmmlated will geaerally have beoi de- 

 stroved bv being C5)raised and toongfat within the famits of 

 the coast-action. 



These remarks apply chieSy to Uttoral and snb-Iittoral de- 

 posits. In the case of an extensive and ^bDow sea, snch as 

 that within a large part of the Malay .\rchipelago, where the 

 depdi varies from 30 or 40 to 60 fathcHns, a wid>dT extended 

 formation might be formed dnring a period of deration, and 

 yet not suffer excessively from denodation daring its slow 

 iq^ieaval; bat the thickness of the formation could not be 

 great, fcr owing to the elevarory movemsit it wookl be less 

 than the depth in which it was formed: nor would the deposit 

 be much consolidated, nor be capped by overlying formatiaasy 

 so that it wcnli rm a good chance of being worn away by 

 atmospheric degradation and by the action of the sea during 

 subsequent oscillaticns of leveL It has. however, been sug- 

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

 rising and before being denuded. subsMied. the deposit formed 

 dtrrins^ the rising movement, thoogfa not thick, might after- 

 wards become protectef '" " ""esh accumulatioas. and thus be 

 preserved for a long per 



Mr. Hopkins also expresses his belief that sedmtentarj beds 

 of considerable horizontal extent have r^- ' tij 



destroyed. Bet all geologists, excepting _; :. "^ 



that our present metamorphic schists and pltttomc r . -.- ■ :ice 



