FOSSIL HUiSIULITHS 511 



and are especially abundant in and characteristic of the Tertiary, 

 where they are often associated with brown coal. 



Broi^'n Coal is a compact or earthy, altered peat deposit, espe- 

 cially characteristic of the Tertiary rocks. It represents one of the 

 intermediate stages from peat to mineral coal, and still often shows 

 evidence of its organic origin. It varies from pale brown or yel- 

 low to deep brown or black, though some shade of brown is the 

 prevailing color. It contains from 55 to 75 per cent, of carbon, has 

 a specific gravity of 0.5 to 1.5 and burns easily with a sooty flame 

 and strong odor, leaving a light ash. The most extensive deposits 

 are in the Oligocenic of North Germany, but peat beds altered to 

 Brown coal have also been observed in post-Tertiary deposits. 



Bituminous Coal. This coal, also called soft coal, is found in 

 the Mesozoic and the Carbonic. It is black, compact, usually brit- 

 tle, with cubical or conchoidal cleavage, and has a shiny luster. It 

 contains from 75 to 90 per cent, of carbon and generally some sul- 

 phur. Its specific gravity ranges from 1.2 to 1.35, and it burns 

 with a bright, clear flame. Some varieties cake on burning, others 

 are consumed to ashes. Generally no trace of organic matter is 

 recognizable, except under the microscope. 



Anthracite, or hard coal, is the most highly mineralized form of 

 coal, with a black color, strong, metalloid or vitreous luster and 

 conchoidal fracture. Its specific gravity ranges from 1.35 to 1.7, 

 and it contains over 90 per cent, of carbon. It kindles with diffi- 

 culty, but burns in a strong draught with great heat and without 

 smoke, caking or odor. It occurs in disturbed regions where the 

 volatile matter has been driven ofif through heat and metamorphism. 

 Some anthracites also originate through extensive loss of the vola- 

 tile gases before entombment. 



Graphite, or pure carbon, is found chiefly in ancient crystalline 

 rocks, such as gneisses, mica schists, metamorphic limestones, etc. 

 When originating from organic matter it is the product of extreme 

 metamorphism, but it may also be formed in purely inorganic 

 manner. 



Ancient Moors. 



Among the moors of past geological time, those of the Anthra- 

 colithic or Carbonic period deserve especial attention, for they have 

 not only furnished a large part of the coal supply of the world, but 

 their wonderful luxuriance of growth and strangeness of type in- 

 vest them with peculiar interest, and make the restoration of 

 these ancient swamps and forests and their subsequent burial a 

 problem full of fascination. 



