I9II.] STEVEXSOX— FORMATIOX OF COAL BEDS. 107 



beds were formed of transported vegetable matter deposited in 

 basins of deep water. In this later memoir, he discusses the laws 

 governing deposition of inorganic materials of varying density and 

 shape, on lake bottoms in tranquil water, on beds of streams and on 

 shores exposed to the action of waves. This completed, he applies 

 the ascertained principles to explain the formation of coal deposits. 



The basins in which those deposits were laid down were ordi- 

 narily gaping faults, very long except where divided transversely 

 b}- uplifted granite, and, in many cases, the fault is still apparent. 

 Streams began to flow into the basins at once. Where the fault 

 valley was divided transversely by uplifted granite, lake basins were 

 formed like Commentry, Alontvicq, etc., in which the beds are irreg- 

 ular. At other times the fracture valley retained its length and was 

 wide enough to be a strait or estuary, common to several rivers and 

 bordering on seas extensive enough to be aft'ected by tides and waves. 

 Respecting the latter he makes the frank remark : " It is hardly pos- 

 sible to admit that the areas of coal deposit were in direct commu- 

 nication with the high sea, because high-level floods are little com- 

 patible with free access of this [the ocean] ; now, the floods are a 

 condition, sine qua iion, of vegetable contributions; it is necessary, 

 then, to admit that the areas of deposition were lagoons, sheltered 

 from the ordinary tides, fronted by vast low plains, themselves 

 above the tides and furnishing few coarse elements to the river 

 load." 



Other basins retaining their length, were less afifected by marine 

 conditions, possibly because of the narrowness or because of varia- 

 tions in level. Of such is the great syncline extending from Moulins 

 to Decazeville. The deposits are lacustrian. The form of the 

 depression aft'ects the speed of currents and therefore the type of 

 deposits; if broad, the rivers from diiTerent points form deltas, but 

 if narrow, the speed along the middle is such as to sweep away such 

 deposits. The contrasting conditions are shown by the Saint-Etienne 

 and Rive-de-Gier divisions of the Loire coal basin. 



The vegetable matter, to form coal beds, was brought in mostly 

 during floods ; some of it remained afloat ; some was held in sus- 

 pension ; while some, which had undergone thorough maceration, 



107 



