SAPROPELITHS 479 



quiet waters, since strong agitation of the water results in the 

 mclusion of much oxygen and the consequent complete oxidation of 

 the organic matter — a feature observed in strongly agitated lakes. 



The decaying vegetal matter rarely accumulates in any great 

 quantity as an absolutely pure caustobiolith. Most commonly inor- 

 ganic or organic mineral impurities are present in greater or less 

 quantity. Among them clay or mud is often a very important 

 constituent, forming argillaceous sapropeliths (if the clay is of 

 small amount) or more commonly sapropelargilliths or in general 

 sapropellutytes. Lime of clastic or organic origin may form the 

 admixture producing sapropelcalc rocks (sapropelitic calcilutytes, 

 sapropelitic calcipulverytes, etc.), while silica, especially that of 

 diatoms, produces a siliceous or diatom sapropelith. Marine sapro- 

 pelargillites are common on many shallow sea coasts, especially in 

 protected areas, where they constitute deposits of black mud. These 

 mud flats exposed at low tide are extensive generators of hydrogen 

 sulphide, which leads to the precipitation of sulphides, especially 

 those of iron. In this way the foundations are laid for the forma- 

 tion of highly carbonaceous lutytes or black shales rich in iron 

 pyrites and with the remains of a more or less depauperate fauna. 

 Such deposits are forming in the estuaries along the Atlantic coast, 

 and in a fossil state these seem to be represented in part at least by 

 the Devonic Genesee shale of New York State. They are further 

 forming in the lagoons behind the coral reefs of Florida, and in a 

 fossil state these are represented by the Middle Devonic Marcellus 

 shale of New York, and perhaps to a certain extent by the Utica 

 shales of eastern North America. Again they are forming to-day 

 in the depths of the Black Sea, and this type appears to be repre- 

 sented by the Permic Kupferschiefer of Thuringia, and possibly 

 the oil shales of the Calciferous series (Lower Carbonic) of Scot- 

 land. The Posidonia shales of the Jurassic of Europe, and 

 some of the Upper Devonic (Portage) shales of New York have 

 also been interpreted on this basis. (Pompeckj-31 and Clarke-9.) 

 This interpretation is, however, questionable. The black shales of 

 southern United States, i. e., the Chattanooga, are probably more 

 nearly referable to the class of argillaceous humuliths. The various 

 fossil sapropellutytes furnish oil on distillation and may in part be 

 the source of the petroleum in the underlying rocks. 



Purer sapropeliths from the Tertiary are known as Dysodil 

 (Greek SvawSrjs = ill-smelling), on account of their bad odor on 

 burning. Carbonic sapropeliths are represented by Cannel coal, a 

 characteristic of which is that it burns with a bright flame. Both 

 Dysodil and Cannel coal are, however, commonly impure, the im- 



