230 EDWARD C. JEFFREY 



in the bottoms of our existing lakes afford the real elucidation 

 of the mode of formation of coal beds. As in our actual bodies 

 of water, which accumulate vegetable deposits, the nature of the 

 material laid down varies with the depth, tranquillity of the water, 

 and other conditions, so the nature of coals derived from similar 

 formations of past ages varies in composition. Where the spore 

 material is more abundant, the result is a cannel or an oilshale. 

 Where it is still plentiful but not superabundant, we have coking 

 and gas coals as a product. - Where poverty is manifest in the 

 spore content, lean or ordinary bituminous coals are formed. The 

 processes of devolatilization leading to the formation of anthracites 

 and similar high-grade coals will not be considered in the present 

 connection. 



