COAL. 313 



difficulties ; yet, in this case, the necessity of similar 

 changes is equally demonstrated. But if, as I for- 

 merly suggested, a gradual subsidence of the land 

 during this condition of the earth is admitted, the 

 difficulty respecting successions of any depth, ceases, 

 as unequal subsidences would aid in accounting for 

 unequal depths : while such a possible state of things 

 is supported by the phenomena of Ban da already no- 

 ticed, and by much more that 1 need not here repeat. 

 It is not difficult to explain the presence of marine 

 bodies, or even of complete marine strata, if such 

 there really are in any coal series. It is merely to sup- 

 pose an aestuary instead of a lake ; and it has already 

 been shown that the mode of deposition, and the alterna- 

 tion of the substances,, are at present similar in both. 



From the marine origin of the strata above the 

 coal series, it has formerly been shown, that thovse 

 parts of the surface which were once above the water, 

 and which received the deposits of land vegetables, 

 have been subsequently immersed beneath an ocean 

 during the period of unknown, but great duration, re- 

 "quisite for the accumulation of such enormous masses. 

 The last change restored to the surface of the earth, 

 and often to great elevations, those strata which had 

 once before occupied it ; accompanied by all those 

 which are found above it, and by many of those which 

 lay below. Such changes could not have taken place 

 without violence and derangement ; and to them we 

 must attributethose fractures, dislocations, and flexures 

 of the coal strata, no less than those of the other rocks 

 which have undergone analogous changes. 



The ceconomical management of coal strata, and the 

 art of mining them, form a subject foreign to the ob- 

 jects of this work ; and they may be found in nume- 

 rous treatises written for that end. 



