298 THE BORDERLAND OF SCIENCE. 



This is a fact which seems at a first view altogether 

 perplexing; but, as nearly always happens with the 

 more perplexing features of any natural enigma, 

 geologists have been led by this difficulty to the 

 interpretation of the enigma. It is to this very fact 

 that we owe the most trustworthy information yet 

 obtained respecting the process by which coal-beds 

 were originally formed. The solution of the difficulty 

 is due to the same eminent geologist from whom I 

 have already quoted the statement of the difficulty. 

 'The enigma,' he says, 'however perplexing at first 

 sight, may, I think, be solved by attending to what is 

 now taking place in deltas. The dense growth of 

 reeds and herbage which encompasses the margins of 

 forest-covered swamps in the valley and delta of the 

 Mississippi, is such that the fluviatile waters, in passing- 

 through them, are filtered and made to clear themselves 

 entirely before they reach the areas in which vegetable 

 matter may accumulate for centuries, forming coal if 

 the climate be favourable. There is no possibility of 

 the least intermixture of earthy matter in such cases. 

 Thus, in the large submerged tract called the ' Sunk 

 Country,' near New Madrid, forming part of the western 

 side of the valley of the Mississippi, erect trees have 

 been standing ever since the year 1811-1812, killed 

 by the great earthquake of that date ; lacustrine and 

 swamp-plants have been growing there in the shallows, 

 and several rivers have annually inundated the whole 

 space, and yet have been unable to carry in any sedi- 

 ment within the outer boundaries of the morass, so 



