STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 3 



The conditions described by Mantell recall those seen by RusselP 

 on the Yahtse of Alaska. That stream, issuing as a swift current 

 from beneath a glacier, invaded a forest area and surrounded the 

 trees with sand and gravel. Some stems, still retaining their 

 branches, projected above the mass but most of the decaying trunks 

 had been broken ofif by the wind and entombed in prostrate position. 

 The phenomenon is familiar to all who have travelled along rivers 

 with broad bottoms. Lyell states that the top beds of the Port- 

 landian or middle division of the Upper Oolite, containing marine 

 shells, were covered with fluviatile muds on which Zamia and cycads 

 grew.^ He remarks that each dirt bed may represent a notable 

 period of time; 2 to 3 feet of vegetable soil is the only product of 

 very old tropical forests. 



The Kimmeridge Clay, at base of the Upper Oolite, contains, 

 according to Phillips,* a highly bituminous shale, which is utilized 

 as fuel at Kimmeridge on the Purbeck coast. As shown in clififs 

 near that place, the clay, finely laminated and grayish-yellow, with 

 remains of plants and animals, passes gradually into a bituminous 

 shale, which is dark brown, lusterless, slightly calcareous and burns 

 with a smoky flame. Lyell^ states that this sometimes becomes an 

 impure coal and that in Wiltshire it resembles peat. Plant remains 

 are rare and the bitumen may be due, at least in part, to animal 

 matter. 



The coal at Brora in Scotland belongs to the Great Oolite or 

 highest division of the Lower Oolite, which in that region is a mass 

 of sandstones and shales. The seams at Brora are thin, but one 

 of them was worked many years ago for local use. This petty area 

 was described by Murchison, whose measurements are (i) fossil 

 shells, marine, quartz grains, carbonaceous matter, all cemented by 

 calcareous material, passing downward into a mass of compressed 

 leaves and stems, in turn becoming shaly coal, 2 feet, 7 inches; (2) 

 coal resembling jet, divided midway by a parting of pyritous, in- 



2 I. C. Russell, " Second Expedition to Mount St. Elias," 13th Ann. Rep. 

 U. S. Geo!. Survey, 1893, Part I., p. 14, PI. XII. 



3 C. Lyell, " Elements of Geology," 6th ed., New York, 1866, pp. 391-393- 

 4 J. Phillips, "Outlines of Geology of England and Wales," Part I., 1822, 



pp. 127, 128. 



5 C. Lyell, " Elements," p. 394. 



