Geological Society. 431 



ford in Yorkshire, of continuous stems and leaves of Stigmariae, dif- 

 fering from those lately observed by Mr. Logan only as to the greater 

 vertical range to which the leaves extended. Mr. Logan has traced 

 them in a vertical direction seven or eight feet from the stem, and 

 more than twenty feet horizontally *, and concludes that it is im- 

 possible to account for these phasnomena by any theory of drift. 

 He further supposes the Stigmaria to be the plant of which fossil 

 coal is mainly composed. 



I think we may derive, from the important facts above quoted, a 

 probable illustration of the processes by which the formation of a 

 coal-field has been conducted. We may assume the areas now co- 

 vered with coal to have been extensive flats and estuaries, receiving 

 at intervals, during seasons of flood, large deposits of silt and sand, 

 interspersed with leaves and broken branches and trunks of trees, 

 drifted down with the detritus of not far distant lands. We may 

 conceive large portions of the surface of these sedimentary deposits, 

 after the cessation of the floods by which they were respectively 

 transported, to have become the site of broad and shallow ponds 

 or lagoons, which were speedily filled with a matted mass of floating 

 stems and leaves of Stigmaria, to the exclusion of all other plants, 

 in the same manner as the social plant, Stratiotes aloides, now crowds 

 the ditches and shallow ponds in Holland, until the water is filled 

 with a dense assemblage of individuals of this single species, leaving 

 no intervals for the growth of any other plants. We may further 

 admit, that by the deposition of mud or silt between the stems and 

 leaves of Stigmaria, the bottom of each lagoon might have been 

 overspread with the earthy sediments that compose the beds of fire- 

 clay immediately below the coal ; and that the same lagoon, after 

 the deposition of these sediments, continued crowded with Stigmariae, 

 accumulating on one another until they had entirely filled the lagoon 

 with a matted mass of stems and leaves, as modern shallow lakes 

 are gradually filled up and converted into peat-bogs. The surface 

 of the lagoon thus changed to a morass may forthwith have become 

 covered with a luxuriant growth of marsh plants, e.^. with Calamites, 

 Lepidodendra, Sigillariae, &c., the exuviae of which formed a super- 

 stratum of vegetable matter convertible to coal, resting upon a sub- 

 stratum composed exclusively of remains of Stigmariae. The re- 

 gions which were the site of this vegetable growth may, by success- 



• Mr. John Craig, of Glasgow, in an excellent paper on the coal forma- 

 tion of tiie West of Scotland read to the British Association at Glasgow, 

 J 8 10, remarks that " the Sliymuria ficoides is frequently found in the shales, 

 with the leaves attached to the stem and spread out laterally, in a manner 

 which never could have occurred bad the plant been drifted from a distance. 

 The ripi)le-niarks also (he adds), which are observable on almost all tho 

 shales and laminated sandstones throughout the wiiole carboniferous forma- 

 tion, show that these portions of the coal strata were deposited in very 

 shallow water." 



I learn from Mr. Binncy that stems and leaves of Stigmaria abotmd in 

 the beds of clay or fine sand that lie immediately below many beds of coal 

 ia the district of Manchester. 



