GEOLOGY. 309 



earthy particles and sand throughout areas of very great extent, is a fact 

 which has naturally appeared very difficult to explain, if we attribute 

 each coal-seam to a vegetation growing in swamps, and not to the drifting 

 of plants. It may be asked how, during river inundations capable of 

 sweeping away the leaves of ferns, and the stems and roots of sigillaria? 

 and other trees, could the waters fail to transport some fine mud into the 

 swamps ? One generation after another of tall trees grew with their roots 

 in mud, and after they had fallen prostrate, and had been turned into coal, 

 were covered with layers of mud, (now turned to shale,) and yet the coal 

 itself has remained unsoiled throughout these various changes. The lec- 

 turer thinks this enigma may be solved by attending to what is now 

 taking place in deltas. The dense growth of reeds and herbage which en- 

 compasses the margins of forest- covered swamps in the valley and delta of 

 the Mississippi is such that the nuviatile 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 favorable. There is no possibility of the least in- 

 termixture 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 stand- 

 ing ever since the year 1811-12, killed by the great earthquake of that 

 date ; lacustrine and swamp plants have been growing there in the shal- 

 lows, and several rivers have annually inundated the whole space, and yet 

 have been unable to carry in any sediment within the outer boundaries of 

 the morass. In the ancient coal of the South Joggins, in Nova Scotia, 

 many of the underclays show a network of stigmaria roots, of which 

 some penetrate into, or quite through, older roots which belonged to the 

 trees of a preceding generation. Where trunks are seen in an erect posi- 

 tion buried in sandstone and shale, rooted sigillaria3 or calamites are often 

 observed at different heights in the enveloping strata, attesting the growth 

 of plants at several successive levels while the process of envelopment 

 was going on. In other cases there are proofs of the submergence of a 

 forest under marine or brackish water,* the base of the trunks of the sub- 

 merged trees being covered with serpulte, or a species of spirorbis. Not 

 unfrequently seams of coal are succeeded by beds of impure bituminous 

 limestone, composed chiefly of compressed modiola? with scales and teeth of 

 fish, these being evidently deposits of brackish or salt-water origin. The lec- 

 turer exhibited a joint of the stem of a fresh- water reed (Arundinaria ma- 

 cfosperma} covered with barnacle?, which he gathered at the extremity of the 

 delta of the Mississippi or the Baiize. He saw a cane-brake (as it is called in. 

 the country) of these tall reeds killed by salt-water, and extending over sev- 

 eral acres, the sea having advanced over a space where the discharge of fresh 

 water had slac ened for a season in one of the river's mouths. If such reeds 

 when dead could still remain standing in the mud with barnacles attached 

 to them, (these Crustacea having been in their turn destroyed by a return 

 of the river to the same spot,) still more easily may we conceive large and 



