BIOGENIC ROCKS 281 



Caustobioliths. 



I. Sapropelites, (rairpos (sapros), rotten; 7rr;Xos (pelos), slime, 

 mud; iTiys (ites), derived from. These are derived from the 

 decaying organic matter of water organisms, both animal and plant, 

 alg?e, etc.'^ (sapropel, Faulschlamm, decay ooze, putrid slime). 

 When formed into rock they constitute sapropeliths or sapropelites.f 

 They differ from the humus rocks in their greater content of fat 

 and protein. 



2. Humus and Humulith. These are deposits derived from de- 

 caying land plants, including those of swamps and marshes. Car- 

 bohydrates are an important product of the decay of the higher 

 plants. All peat and coal deposits belong here. Lithified, they form 

 humus rock or chamaeliths (x"/^* on the ground, Greek equiva- 

 lent of humus; the Latin would be humulith) . 



3. Liptohiolith, Xewrw (leipo)^ XewrTos (leiptoSj Latinized, Hp- 

 tos^ left behind, residual and biolith). These comprise the resins 

 and gums, amber, copal, etc., which, from their greater resistance to 

 decay remain behind after the destruction of the plants contaming 

 them. 



Subdivision of Hydrogenic and Biogenic Rocks. In both 

 hydrogenic and biogenic rocks the chemical division is most readily 

 made on the basic elements of the salts. In texture hydrogenic 

 rocks are both crystalline and amorphous while in biogenic rocks the 

 amorphous texture predominates. 



Textures of Amorphous Hydrogenics. Among the amorphous 

 hydrogenics the following subtextures are most marked : 



(a) Botryoidal, with grape-like, rounded surfaces. 



(b) Pisolitic, of large spherules. 



(c) Oolitic, of small spherules, also characteristic of the bio- 



genic rocks. 



(d) Banded, as in stalactic deposits (stalactites and stalagmites). 



(e) Lam,inated, or scaly. 



(f) Fibrous. 



(g) Concretionary. 



(h) Tufaccous, as in calcareous and siliceous, tufa or sinter. 

 Textures of Biogenic Rocks. Among the biogenic rocks we note 

 the following subtextures: 



* Mineral structures, such as shells and skeletons, are of course excluded, 

 t The termination pelite should be restricted to oozes or slimes of endogenetic 

 origin, leaving the termination lutyte for oozes of exogenetic or clastic origin. 



