Handbook of Paleontology 21 



known as crinoidal limestones. Of all the parts of the 

 animal, bases, stems and parts of stems are generally 

 most abundant and prominent. In the upper part of 

 the Becraft limestone (Lower Devonian) of New York 

 crinoid bases are so abundant that formerly the name 

 Scutella or Encrinal limestone was given to the for- 

 mation. The Tichenor limestone (Middle Devonian) 

 between the Moscow and Ludlowville divisions (as 

 previously denned) of the Hamilton in western 

 New York is another such a crinoidal limestone; and 

 there are crinoidal layers in the Niagaran (Silurian) 

 beds. Other instances of rock formed through organic 

 agency, such as limestone beds rich in phosphate formed 

 through the accumulation of the bones of vertebrate ani- 

 mals, might be mentioned, but the above examples are 

 among the most important. 



Accumulations formed directly from organic tissues 

 may be of plant or animal origin. Plant material that 

 is buried in a marsh or swamp decays very slowly giv- 

 ing off carbon dioxide (C0 2 ), water (H 2 0) and marsh 

 gas (carbon and hydrogen, CH 4 ) until the proportion 

 of carbon is relatively increased. As this change goes 

 on, together with the pressure of overlying material, 

 the plant tissues pass through various stages of coal ; 

 and if the process is continued far enough all other 

 substances except the carbon may be driven off leav- 

 ing pure carbon or graphite, some of which is due to 

 purely inorganic, chemical processes. Peat is the first 

 product in the partial decay of vegetable matter. 

 Brown coal is an altered peat deposit and still shows 

 signs of its organic origin. It is common in Tertiary 

 formations. Lignite is found in beds of Tertiary and 

 Mesozoic age. It is altered woody tissue which is gen- 



