242 PHYSIOGRAPHY. [chap. 



in lycopodium spores; and, by thus coating them with a 

 resinous powder, enables them to roll over the tongue with- 

 out direct contact with its moist surface. And, before the 

 days of the electric light, the stage-manager was in the 

 habit of using this highly combustible resinous material, 

 under the name of " vegetable brimstone," to produce a 

 blaze of mimic lightning. 



From what has now been said, it appears probable that 

 most coal has been formed in something like the following 

 way A foiest of lepidodendrons, sigillarias, ferns, and other 

 plants, grew up on an old land-surface, which is now repre- 

 sented by the under-clay, or its equivalent. Season after 

 season, showers of spores fell from these flowerless plants, 

 and, accumulating on the soil, became mixed with the 

 fallen fronds, and with larger or smaller portions of the stems 

 of the surrounding trees. While a large proportion of the 

 soft vegetable matter slowly disappeared by decay, or left 

 only a highly carbonized residue, of which the part that 

 retains a recognizable structure is the " mother of coal," the 

 resinous spores resisted decomposition, and remain dis- 

 tinguishable in all the less altered coals. The roots of the 

 Lepidodendra were often preserved by the clay in which 

 they grew, and became the fossil stigmaria. 



When a layer of vegetable soil had thus accumulated 

 to a considerable thickness, the land slowly subsided, and 

 the old forest was buried beneath deposits of mud and 

 sand, which have since hardened into shales and sand- 

 stones. Compressed beneath these sediments, the vege- 

 table matter underwent peculiar changes, which resulted 

 m the formation of coal. Then a time came when the 

 sedimentary deposits were upheaved, and another forest 

 sprang up on the new land, forming a second bed of 

 coal. Hence every seam of coal indicates fresh movement 



