Geological Society. 435 



coal has been formed ; and the occasional assemblage of large num- 

 bers of cones and seed-vessels of the same species, e.g. of Lepido- 

 strobus and Trigonocarpum,upon one spot, seems to indicate that they 

 dropped into their present place from the trees on which they grew. 



Should the above hypotheses be correct, we may expect to find 

 corresponding differences of organic structure on niicroscopic exa- 

 mination of the vegetable remains in the lower and upper portions 

 of many beds of coal ; and the attention of observers may at this 

 time be profitably directed to the examination of thin slices of coal, 

 carefully selected from different regions of the same bed, for the 

 purpose of ascertaining whether differences exist between the com- 

 ponent vegetables of tlie upper and lower regions of individual 

 strata, sufficiently obvious and constant to justify us in referring the 

 lower region of certain strata to a sub-aqueous, and the upper re- 

 gion to a sub-aerial origin. Should an entire bed of coal exhibit 

 no other vegetable structure than that of Stigmaria, it may be 

 inferred that these plants had not so far filled up the lagoon in 

 which they grew, as to convert it to a sub-aerial swamp, before fresh 

 floods of water from the land overwhelmed these sub-aqueous ve- 

 getables with sand and silt. Should we find another coal-bed with- 

 out any Stigmaria, and interspersed through its whole vertical ex- 

 tent with Calamites and otlier sub-aerial plants, indicating a sM'ampy 

 soil, we may conclude that the vegetables whicli formed this bed of 

 coal grew upon humid and swampy flats adjacent to lagoons ; and 

 that whilst the latter were accumulating beneath their shallow waters 

 the materials of a future bed of coal, formed exclusively of the 

 aquatic Stigmaria, the adjacent flats were simultaneously accumula- 

 ting materials destined for a similar function from the sub-aerial 

 swamp-plants of the same era. But in the compound case of coal 

 formed by the conversion of a shallow lagoon into a morass, we 

 should find in the lower portion, next above tlie fire-clay, no other 

 plants than the aquatic floating Stigmaria, and in the upper region 

 of the same bed no traces of Stigmaria, but many kinds of sub- 

 aerial plants ; whilst in its middle region we should discover a con- 

 tact of aquatic witli sub-aerial plants. 



We may explain the frequent occurrence of erect trees immedi- 

 ately above the upper surface of a bed of coal, as in the cases m'c 

 have spoken of near Bolton and Chesterfield, by supposing the roots 

 of these trees to have found support and nutriment in the entangled 

 remains of other plants which had preceded them on tlie same spot, 

 as the Scotch firs grow in ])eat witiiout touching any subsoil ; but 

 cases of trees tlius standing erect are comparatively rare exceptions 

 to their ordinary state of prostration, caused eitlier by decay or tem- 

 pests, or by the violence of the currents that submerged and buried 

 witii sand and silt the morasses in which they grew. 



Fragments and large stems of trees that are found truncated at 

 botli ends, and inclined in all directions in thick beds of sandstone, 

 like the coniferous trees at Craigleith and Newhaven, near Edin- 

 burgh, seem to liave been torn from their native bed and drifted 

 with tiie sand to tlie [)lace in which they are now imbedded. 



Mr. Logan and Mr. L. L. Dillwyn have discovered ])ebblcs or 

 Fhil. Mag. S. 3. Vol. 20. No. 132. May 18*2. 2 G 



