188 ON THE ORIGIN OF COAL. 



Coal seams occurring in a short distance, from 

 the compound nature of some of the seams, and 

 from the abundance of casts of a Cypris, mingled 

 with the remains of large fish. The black line 

 here also marks the rate of subsidence of the 

 crust of the earth, and the velocity of the water, 

 as in the other section. 



Both sections are taken for the purpose of 

 proving the hyj. ^thesis, that the currents of water 

 which carried the arenaceous, argillaceous, and 

 calcareous deposits of the coal measures, were 

 caused chiefly by subsidence of the bottom of the 

 sea, and that seams of Coal indicate periods of 

 rest, during which such currents ceased to flow, 

 and thus allowed of the growth of vegetable 

 matter, sufficient for their formation. 



The first section (see plate III, fig. 1,) com- 

 mences with the floor of the " Parson's Mine," 

 which is composed of a crystalline stone, known 

 by the name of Gannister. It is formed of a fine 

 grained silt, cemented together by a silicate of 

 lime or alumina, and contains an abundance of 

 tree roots, (Stigmaria ficoides) evidently in situ. 

 When these trees grew, the soil which supported 

 them could no*- have been deeply covered with 



