STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 55 



marine Cretaceous, but is of fresh-water origin, the animal remains 

 being indeterminate bones with shells of fresh-water mollusks. 

 Plant remains and silicified stems are in the clays. The lignite is 

 described as compact, blackish brown and lusterless. 



The Wealden of Hanover, that portion equivalent to the Hast- 

 ings sand of England, has coal seams, which in many places have 

 economical importance. The region^ has been studied by several • 

 geologists, each having in view the study of some special features. 

 The area has extreme length from east to west of about i6o miles 

 and an extreme width of about 120 miles from north to south. 

 Exposures are not continuous, for erosion has removed the Wealden 

 from extensive spaces, while in others the surface rocks belong to 

 later formations. According to Credner, it reaches from the Harz 

 Mountains westward to the Holland border, where it passes under a 

 thick cover of diluvium. The exposed areas are isolated and at 

 times are so widely separated that sections have little resemblance. 

 The Wealden consists of clays, marls, sandstones and coal beds ; the 

 colors are from white to gray, with rare bands colored by oxide of 

 iron. Dunker states that the coal usually resembles the older black 

 coals, the plant materials have undergone much greater change than 

 in brown coal, and distinct woody structure is rarely recognizable. 

 Some mines yield a coal comparable to the best in England ; a sample, 

 analyzed by Regnault, gave carbon, 89.50; hydrogen, 4.83; oxygen 

 and nitrogen, 4.67 ; ash, i. This type is dense, brilliant, with uneven 

 to conchoidal fracture and in appearance resembles anthracite. It 

 is closely jointed and usually has a blackish brown streak. But 

 there is lignite in the Wealden, with woody structure and reddish 

 brown streak. A sample from Helmstadt, analyzed by Varrentrapp, 

 yielded carbon, 68.57; hydrogen, 4.84; oxygen and nitrogen, 19.87; 

 [ash, S.yz]. Dunker thinks this brown coal derived from conifers, 

 cycads, lycopods and ferns. 



In the Osterwalde, a very different type, the Blatterkohle, is 



5 W. Dunker, "Monographic der Norddeutschen Wealdenbildung," Braun- 

 schweig, 1846, pp. xi-xxviii, 2, 21 ; Heinrich Credner, " Ueber die Gliederung 

 der oberen Juraformation und der Wealden-Bildung im nordwestlichen 

 Deutschland," Prag, 1863, pp. ix, 47-54. ^32, 138. I33. 138-141 ; C. Struckmann, 

 " Die Wealden-Bildungen der Umgegend von Hannover," Hannover, 1880, pp. 

 14-28, 30-36. 



