482 PRINCIPLES OF STRATIGRAPHY 



anthracite coal, and, moreover, the two may become interstratified, 

 the one or the other predominating, according to the length of time 

 during which the conditions responsible for either existed. Where 

 the beds are relatively thin the coal is spoken of as banded cannel 

 or bituminous coal, as the case may be. A section from Reckling- 

 hausen in Westphalia illustrates a complex relationship. In de- 

 scending order we find : 



5. Bituminous coal about 10 cm. 



4. Banded coal about 95 cm. 



3. Cannel coal about 8-15 cm . 



2. Banded coal about 10 cm. 



I . Cannel coal about 1.3m. 



This section shows, first, a water body in which algae and other 

 truly aqueous plants lived and accumulated as decomposition slime, 

 followed by marshy conditions with growth of higher plants, but 

 with repeated inundations to furnish the decomposition slime from 

 which the bands of cannel coal were formed. This is followed by a 

 second period of complete submergence, with the formation of can- 

 nel coal. Then the alternating conditions were repeated, with the re- 

 sult that more banded coals were formed, and the area was finally 

 converted into a marsh or moor with the formation of pure bitumi- 

 nous or gas coal. 



The algous origin of cannel coals has, however, been seriously 

 questioned by Jeffrey (25). He finds, on the basis of numerous 

 well-prepared microscopic sections from widely separated regions, 

 that the organisms found in abundance in boghead coals are not 

 of the nature of colonial gelatinous algse, as has been asserted by 

 Renault, Bertrand and Potonie, but are spores of vascular 

 cryptogams. This, Jeffrey holds, also overthrows the algal hy- 

 pothesis of the origin of petroleum and similar substances, these in- 

 stead having been mainly derived from the waxy and resinous 

 spores of vascular cryptogams laid down on the bottoms of shal- 

 low lakes during the coal period. "These lacustrine layers, either 

 as cannels, bogheads,^ or bituminous shales, according to the sporal 

 composition and the admixture of earthy matter, are the mother 

 substance of petroleum. Pressure and temperature either separ- 

 ately or combined, in the presence of permeable strata, have brought 

 about the distillation of petroleum from such deposits." (Jeffrey- 

 25:^90.) 



Jet (Ger. Gagat, Fr. jais, and jayet). This mineral, for which 

 Giimbel suggested the name gagatite, is a sapropelith obtained in 

 black sapropelargillytes of Mesozoic and younger formations. What 



