STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 17 



the rest being so badly broken by partings as to be worthless. The 

 interval to the conglomerate of Corwin Bluff is filled with shale, 

 holding at least 8 coal seams. The cliff could not be reached and 

 the thicknesses of only three could be estimated : 4, 12 and 30 feet. 

 An irregular seam underlies the conglomerate and rests on sand- 

 stone; it is in pockets but the coal is good in spite of the distortion. 

 Lower seams were seen in the next 1,000 feet, not distorted, as they 

 are in soft shale, which took up the strains. 



Below the lowest seam of the Corwin is a series of barren meas- 

 ures, about 8,000 feet, in which only thin streaks of coal wxre seen ; 

 this overlies the Thetis group, which is reached at 6 miles east from 

 Corwin Bluff and its highest seam is known as the Thetis, 6 feet 

 thick, and opened many years ago. Ten seams were found in the 

 succeeding 700 feet of shale, only two of which are likely to prove 

 important. 



This necessarily imperfect record suffices to show that the quan- 

 tity of Jurassic coal in northwestern Alaska is enormous. Some 

 cannel is said to have been found in the Corwin group, but Collier 

 saw none. 



Jura-Triassic. 



Generally speaking, it may be said that where the succession is 

 complete, there is always a portion of the column,' which is de- 

 batable ground, and there is difficulty in determining the boundary 

 between formations. In some cases, unconformities due to folding 

 or to erosion offer evidence on which to base a final determination ; 

 but such areas, though large in square miles, often mark only local 

 adjustments, similar to those observed within formations, but which 

 no one regards as important. Occasionally, the matter is compli- 

 cated by lack of fossil remains. Such is the condition in a great 

 part of Australia, where it has not been possible to divide satis- 

 factorily the great mass between the Permo-Carboniferous and the 

 Cretaceous. Jack and Etheridge-*' recognize a Trias-Jura system in 

 Queensland, which Jack has divided into the Ipswich and Burrum 

 formations. 



26 R. L. Jack and R. Etheridge, Jr., " Geology, etc., of Queensland," 1892, 

 pp. 300-39, 366. 



PROC. AMER. PHIL. SOC, VOL. LVII, B, JANUARY 30, I918. 



