480 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



The fitage superieur de St.-Etienne, 250 to 350 meters thick, is 

 in an area of 1,000 to 1,500 meters wide by 11 kilometers long. It 

 has 10 or 12 coal seams with total extreme thickness of 15 to 20 

 meters at the east but diminishing rapidly toward the west, where 

 micaceous shales prevail. The lowest seams are of moderate thick- 

 ness and yield inferior coal. The seams in the middle are 2.50 to 7 

 meters and are good. The highest seam, 3 to 10 meters, yields fria- 

 ble coal. In all cases the coal is rich in volatile and appears to be 

 composed of Psaroniocaulon, Stipitopteris and Calamites. 



The upper sterile stage or Permo-Carboniferous, apparently not 

 more than 475 meters thick, consists of shaly green and red sand- 

 stone. The passage from St.-£tienne is gradual and, as far as can 

 be gathered from Gruner's statements, the succession is conformable. 



Gruner notes that the forests of this basin are confined to the 

 Middle St.-fitienne. Long ago, the upper one was described by 

 Alex. Brongniart.^^ Though are rocks are horizontal, they have 

 suffered from a slight movement, which has broken the continuity of 

 many stems, so that the root portion has been shifted. Eighteen 

 vertical stems are shown on the plate, which represents about 75 

 feet of the wall, and roots are distinct on many of them. Brong- 

 niart was confident that this is part of a forest of bamboo-like plants. 

 The interior of the stems is filled with sandstone like that in which 

 they occur; but this is coated by coaly or ferruginous material. 



Gruner says that another forest is at 100 meters lower in the 

 section. He saw in the Treuil mine 12 trunks in a space 12 meters 

 square. These rest directly on the coal, which is not penetrated by 

 the roots, though in some cases they spread out upon it. These are 

 Sigillaria. Similar conditions were observed elsewhere. The rela- 

 tions in the mur are different from those observed in the roof, for 

 at St.-£tienne he saw rootlets descending from the coal into the un- 

 derclay. This condition is especially clear in les Batardes of the 

 Rive-de-Gier, where Stigmaria abound in the mur. His discussions 

 on pp. 168-173 and 483-496 should be consulted by all who are inter- 

 ested in the matter. 



^~ Alex. Brongniart, " The Fossil Vegetables Traversing the Beds of the 

 Coal Measures," Ann. des Mines, 1821 ; translated in de la Beche's " Selec- 

 tion of Geological Memoirs," etc., London, 1836, pp. 208-216. 



