STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 487 



is difficult to conceive how the supply could be maintained in quiet 

 water. It must be remembered that the proportion of dissolved 

 ulmin is very small : Smith^*' ascertained that very brown water con- 

 tains only 4 grains to the gallon, and that if the quantity be 6 grains, 

 the color is intensely dark. 



It should be noted here that the conclusions reached by Bertrand 

 and Renault have been controverted emphatically by Jeffrey and by 

 Thiessen,^'' who employed improved methods of preparing the ma- 

 terial. Jeffrey examined the Autun and other Bogheads and found 

 no algse but abundance of spores. Thiessen's results were very 

 similar. 



Bretagne. — Several small basins have escaped erosion in the area 

 of the lower Loire Riven within Brittany. A general description 

 of them was pubHshed by Barrois about 25 years ago, but his work 

 is not now within the writer's reach. The only available notes are 

 by Rolland,^^ presented many years since. These coals, almost an- 

 thracite, are regarded now as belonging to the Culm. The deposits 

 described by Rolland are said to extend from Doue in Maine-et- 

 Loire to Nort in Loire-Inferieure, about 40 leagues. He divides 

 the section into eight systems, each with a conglomerate at base, the 

 intervening rocks being sandstones and blackish shales. The first 

 five systems, in each case, contain only thin streaks of coal, but the 

 sixth, Goismard, has two seams. Petit and Grand Goismard, which 

 at times unite and are mined. The upper. Petit, averaging about 

 50 centimeters, yields a hard lump coal and has as its roof a sand- 

 stone, pierre carree, almost 70 meters thick. Its faux-toit is fine- 

 grained sand, without cement and about one meter thick ; it passes 

 downward into a loose material, termed "tourte" by the miners 

 and consisting mostly of decomposed feldspar. The mur of this 

 seam, roof of the Grand seam, is shaly sandstone, 6 to 8 meters thick 

 at the outcrop ; at 100 meters down the dip, it is 3 and at 200 it is 

 only- 1 meter. In the deepest portion of the works, the seams have 



86 R. Angus Smith, Manch. Lit. Phil. Soc, III., Vol. IV., 1871, pp. 50, 6^. 



^"^ E. C. Jefifrey, " On the Nature of Some Supposed Algal Coals," Proc. 

 Amer. Acad. Sci., Vol. XLVI., 1910, pp. 273-390; R. Thiessen, "Plant Re- 

 mains Composing Coal," Science, N. S., Vol. XXXIII., 191 1, pp. 537-552. 



88 M. Rolland, " Notice sur le terrain anthraxifere des bords de la Loire," 

 etc., Bull. Soc. Gcol. France, t. XII., p. 463. 



