46 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



kins have testified that, in the cases described by them, the arrange- 

 ment of the rhizomas proved not only that the plants are in situ 

 but also that the direction of prevailing winds was the same during 

 the Carboniferous as now. The immense extent of roots, spread 

 out in normal attitude, as in the plants described by Adamson, Wil- 

 liamson, Potonie and others, compels those students to assert that 

 no conceivable mode of transportation can explain the phenomenon. 

 The interlacing of the roots, shown by Schmitz, Crampton and many 

 others, is regarded as affording strong confirmatory evidence of in 

 situ growth. Many coal beds are divided by clay partings of 

 variable thickness ; Stigmaria, at times, occurs abundantly in such 

 partings. Robb's remarkable specimen was rooted in such a lens of 

 fireclay. But Sigillaria and Lepidodendron, to which Stigmaria 

 belongs, are not the only coal-making plants; just as peat is com- 

 posed of many plants or of different assemblages of plants in various 

 parts of the world, so coal in one area was formed of plants unlike 

 those in another. There are great coal deposits containing no 

 Sigillaria or Lepidodendron and consequently the underclay is with- 

 out Stigmaria. 



Occasionally rootlets are found so arranged as to make certain 

 that the materials had suffered no disturbance. Ward,-^ visiting 

 the Saint-Etienne coal field after the Geological Congress of 1900, 

 saw many instances in which the finest fibrils of roots of erect 

 Calamites passed across the planes of bedding down the con- 

 glomerate, which formed the original floor; the condition was re- 

 garded by him as incompatible with the slightest movement. 

 Bertrand^^ observed rootlets in situ in an underclay within the 

 Grande Couche at Decazeville ; and the writer saw threads of coal 

 descending into an underclay in the upper part of the Campagnac 

 coal bed of the same basin, which suggested rootlets. Fox-Strang- 

 ways"** states that he saw rootlets passing downward from the Four- 



^ L. F. Ward, " The Autochthonous or Allochthonous Origin of the Coal 

 and Coal Plants of Central France," Science, N. S., Vol. XII., 1900, p. 1005. 



"P. Bertrand, in letter of January 15, 191 1. 



'' C. Fox- Strangways, "Geology of South Leicestershire and South Derby- 

 shire Coal Field." Mem. Geol. Surv., 1907, p, 52. 



