VALUE OF FLORAL EVIDENCE 225 



parts — that is, seed envelopes, spore covers, pollen shells, and fragments 

 of wood and stems, especially of resinous or very dense types. This is 

 due to several causes: 



1. On account of their fragility leaves, especially those of ferns, are 

 very quickly rumpled, curled, torn, or shredded in water transport, and 

 if long en route are soon reduced to fine refuse ("Hacksel") by wind, 

 wave, or current action. Leaves become submerged sooner than trunks, 

 twigs, etcetera; they are promptly attacked by the pelagic animal life, 

 and their mesophyll quickly decays as the result of microbian action. 



2. On reaching salt water they are very quickly covered by slimes, 

 animal and vegetal organisms, which coat or corrode the surface, so that 

 unless buried promptly they can not leave clean or clear-cut imprints, 

 even if submerged beneath cold waters. The observations of several 

 marine naturalists go to show that signs of the destructive agencies, ex- 

 clusive of wave and current, are generally evident in less than two days 

 from the moment of marine submersion. 



3. Decay proceeds more rapidly in salt than in fresh water, by reason 

 of the abundance and variety of the attacking animal types, and also, it 

 is said,^° on account of the greater amounts of sulphates and carbonates 

 in sea water, which by decomposition in the presence of organic acids 

 facilitate the oxidation (destruction) of the plant tissue. Decay proceeds 

 even at great depths and in low temperatures; but these are regions of 

 slow deposition, so that there is correspondingly greater time for corro- 

 sion and putrefaction, or even total destruction, before the organic matter 

 becomes protected by an oxygen-excluding sedimentary cover. 



4. The conditions of open marine deposition preclude the development 

 of a partial or completely aseptic or toxic water-cover, such as may take 

 place in fresh or land-locked water bodies. 



5. Eegions of distinctly calcareous deposition, or of limestone forma- 

 tion — that is, regions comparatively free from terrigenous sediments — ; 

 are apt to be far from the mouths of rivers and from currents carrying 

 land sediments, therefore plants are not likely to reach them in good con- 

 dition unless the deposits are close to shore or coast. If rapidly trans- 

 ported they are liable to damage by wave action and other commotion of 

 the current. Furthermore, in most regions of such sedimentation the 

 accumulation of the rock-forming material is so slow that the most en- 

 during parts of the plants may seldom escape decay before they are so far 

 buried as to make permanent their forms. 



The fresher the vegetal material the better the chances that some pcr- 



19 Challenger reports : Deep-sea deposits, p. 256. 



