24 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



shire, etc." Limestones with marine fossils are found at various 

 horizons in the Donetz section. The presence of an underclay proves 

 nothing — even though Stigmaria ficoidcs be the only plant present 

 for a confused assemblage of plants is seen above and below the coal 

 beds and the fossil beds are exclusively marine. The fine underclay 

 indicates only that the sea bottom was covered with detritus of plants 

 washed in by floods ; the heavier earthy matters, accompanying the 

 detritus, sank to the bottom, while the plants floated and formed the 

 upper stratum. Those plants, thus left on the muddy slime, were 

 covered afterwards by other sediment. ]\luch of the coal, in strata 

 alternating with marine sediments, may have come from the wash- 

 ing away and sinking into the sea of floating masses of matted earth 

 and plants. 



At a later date,^* he discussed the question more broadly. He 

 refers to the terrestrial conditions exhibited in the Upper Carbonif- 

 erous of England and to the lack of a physical break there between 

 the Lower and the LTpper Measures, such as appears in Germany and 

 France. In those countries, the later accumulations may well be 

 accounted for by depressions of low woodlands and jungles beneath 

 freshwater, followed by elevations and depressions. There is no 

 physical break in Britain, but there is the same passage from 

 marine to terrestrial conditions, of which the coal beds offer posi- 

 tive evidence; for the roots of SigiUaria are found in the underclay, 

 which was the soil of a primeval marsh or jungle. The view, which 

 supposes many and successive subsidences of vast swampy jungles 

 beneath the level of the waters, best explains how the different 

 organic masses became so covered w^th beds of sand and mud, as to 

 form the sandstone and shale of such coal fields. But this theory of 

 oscillations . . . can scarcely have an application to those other 

 seams of coal, which, as before mentioned, are interstratified with 

 beds containing marine shells, the animals of which, such as Prodiicti 

 and Spirifcrs, must have lived in comparatively deep water." 



He conceived that the latter class is to be explained only by 

 the supposition that great rivers, flowing through lowlands, trans- 

 ported vast quantities of trees, etc., entangled in earth, and de- 



^* " Siluria," 3d ed., London, 1859, pp. 315-317. 



24 



