478 PRINCIPLES OF STRATIGR.'XPHY 



VEGETAL DEPOSITS. (CAUSTOPHYTOLITHS.) 



The actual accumulations of vegetal matter in the strata of the 

 earth's crust are perhaps of even greater significance than the lime 

 and silica deposits caused by plants. There are few horizons which 

 have not some kind of plant deposit in the form of carbonaceous 

 material. They occur even in the Algonkian, where a bed of an- 

 thracite two meters thick is found in the upper part of the middle 

 Algonkian or Jatulian formation north of Lake Onega in Finland. 



As already noted, Caustophytoliths have been divided into those 

 formed from plants living where their remains are found to-day, 

 autochthonous caustophytoliths, and those transported to their pres- 

 ent place of occurrence, or allochthonous. Autochthonous caus- 

 tophytoliths may be terrestrial or aquatic, according to the condition 

 of life of the plants, i. e., whether land or aquatic plants. Alloch- 

 thonous caustophytoliths are primarily allochthonous, when the ma- 

 terial of which they were made was transported in the living, or at 

 least undecomposed, condition to the place where it is now found, 

 and secondarily allochthonous, when transportation occurred after 

 the plant had become a caustophytolith. 



Modern autochthonous deposits of vegetal matter are found in 

 the sea, especially in enclosed bodies of sea water, in marine 

 marshes, fresh water swamps, and in bogs and wet woods. Alloch- 

 thonous deposits may be found embedded in marine, lacustrine, flu- 

 viatile or even asolian deposits. 



PETROGRAPHICAL TYPES OF VEGETAL DEPOSITS. 

 As noted in Chapter I, vegetal deposits may occur in one or another 

 of the following types: i, Sapropeliths ; 2, Humuliths; and, 3, 

 Liptobioliths. Each of these groups will be considered at some 

 length. 



Sapropeliths. 



These are accumulations of the decaying organic tissues of 

 aquatic animals and plants at the bottom of the sea, or in fresh 

 water lakes and ponds. In the unconsolidated state it is a foul or- 

 ganic slime (Faulschlamni), or slime of decomposing organic mat- 

 ter derived from the water. In so far as plants contribute to this 

 slime, it is of algous origin, since any deposit formed by higher 

 plants normally belongs to the next type, the humuliths. The chief 

 chemical difference between such sapropelitic material and that 

 formed by land and swamp plants is the higher fat and protein 

 content of the former. Sapropeliths accumulate only in relatively 



