STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 57 



those replaced with sandstone or oxide of iron show no trace of 

 structure, but those from the coal resemble Pinus. He believes that 

 much of the coal is derived from conifers. 



Credner reports that the sandstone is 540 to 550 feet thick on the 

 south slope of the Diester range, 8 to 12 miles south from Hannover, 

 where it consists of alternating clay shales, marly shales, sandstones 

 and stone coal ; the chief mass is a yellow, fine-grained sandstone 

 with little cementing material. The section shows 16 coal seams, 

 of which II are less than 10 inches thick and have "bad coal." 

 Three beds, 2 feet, i foot 6 inches and i foot respectively, are of 

 " workable " thickness and yield good coal. Clearly, the periods 

 when coal accumulation was possible, were of brief duration and the 

 general conditions were not such as to encourage formation of good 

 coal; the total thickness is little more than 15 feet, of which less 

 than one third is good. The fauna is fresh-water, Unio, Paliidina, 

 Cypris, Lepidotus and Sphcrrodus being the prevailing forms ; 

 Cyrena is not rare. The flora consists of ferns, cycads, conifers 

 and palms. 



The Osterwalde area is farther west ; its resources had been de- 

 veloped after Bunker's examinations were made. The Wealden 

 sandstone is approximately 500 feet, but the conditions are not the 

 same as in the Diester area. The " workable " coal seam, one foot 

 thick and 28 feet above the base at Diester, is here in the same posi- 

 tion, but only 8 inches thick. Within 72 feet above it are 3 seams, 

 the thickest being 6 feet 9 inches, all absent from the Diester section. 

 Near Minden, 7 miles farther west, the coal is thicker. Meanwhile 

 the character of sediments has been changing, for the sandstone, 

 predominating at Diester, is insignificant here. The change con- 

 tinues westward : at Bentheim and Ochtrup, on the Holland border, 

 one finds only clays and limestones about 800 feet thick ; the lime- 

 stones yield Melania and Cyrena. According to Credner's descrip- 

 tions, it is evident that the coal decreases in the direction of finer 

 sediments. The thick coals of Minden are associated with the one 

 noteworthy sandstone of that area. Both Dunker and Credner note 

 abundance of sphgerosiderite in the rocks associated with coal seams. 



Studies by Dunker and Credner were mostly in the region west 

 from Hannover; Struckmann gave information respecting other 



