MINERALOGY. 413 



which are indicative of great movements in the waters, 

 constitute the formation designated by geologists under 

 the names of Red Conglomerate, New Red Sandstone, 

 Rothe Todt-liegende, etc. They frequently form layers 

 six hundred feet in thickness, and- contain plants belong- 

 ing to the families of Algae or Coniferae, but scarcely 

 ever any remains of organized beings. 



The Carboniferous Formation embraces the exten- 

 sive deposit of the Coal Measures, which, especially in 

 England, are found in different gradations and in im- 

 mense masses. They are mostly rendered impure by 

 the great quantity of sulphur they contain, and therefore 

 coal-mines are subject to take fire from spontaneous 

 combustion, as the sulphur becomes heated and as the 

 gases evolved from it are highly inflamable, they ignite 

 in coming in contact with air or vapor, and communicat- 

 ing their flame to the surrounding strata or beds of coal, 

 large fires are kindled among them. Stone-coal is evi- 

 dently nothing more or less than the remains of the 

 primitive forests reduced, in antediluvian times, to the 

 present form by the severe action of fire. 



The Silurian Formation or System is subdivided 

 into three principal sections. The upper section consists 

 principally of Clay Slate or Shale, Gray wacke, and Sand- 

 stone, placed in strata, which alternate with one another. 

 Limestone is often found among the clay slate strata. 

 No organic remains exist in this formation, but perfectly 

 developed fossilified mollusks and zoophytes, Pectcn 

 grandcevus, Avicule lepida, and Goniatidce are frequent. 

 The middle section is occupied chiefly by a compact, cal- 

 careous rock of a dark color, made up of different shades 

 of gray, and used under the name marble, as the Black 

 Marble of Corsica. To this formation also belong the 



