486 The Four Visible Ingredients, in Banded Bituminous Coal. 



Rogers, H. D. (1843). ' An Inquiry into the Origin of the Appalachian Coal Strata, 



Bituminous and Anthracitic,' pp. 453-544. Plates XIV-XXI. 

 Russell, W. J. (1906). " The Action of Plants on a Photographic Plate in the Dark," 



' Roy. Soc. Proc.,' B, vol. 78, pp. 385-390. London, 1906. 

 Russell, W. J. (1908). " The Action of Resin and Allied Bodies on a Photographic 



Plate in the Dark," ' Roy. Soc. Proc.,' B, vol. 80, pp. 376-380. London, 1908. 

 Seyler, C. A. (1907). "Composition and Analysis of Coal," in Boulton's ' Practical Coal 



Mining,' vol. 1, pp. 67-90. London, 1907. 

 Stevenson, J. J. (1911-13). " Formation of Coal Beds," 'Proc. Amer. Phil. Soc.,' vol. 50, 



pp. 1-116, 519-643 (1911) ; vol. 51, pp. 423-553 (1912) ; vol. 52, pp. 31-162 (1913). 



Also book, published by New Era Co., Lancaster, U.S.A., 1911-13. 

 Stopes, M. C, and Wheeler, R. V. (1918). " Monograph on the Constitution of Coal " 



(based on a paper read before the London Section of the Society of Chemical 



Industry), ' Dept. Sci. Industi'. Research,' pp. 1-58, Plates I-III. London, 1918. 

 Stopes, M. C. (1919). " Discussion of Dr. George Hickling's paper on the Micro- 

 Petrology of Coal," 'Trans. Inst. Min. Engin.,' vol. 56, Part III, pp. 175-183. 

 Strahan, A., and PoUard, W. (1915). "The Coals of South Wales: with Special 



Reference to the Origin and Distribution of Anthracite," Ed. 2, ' Mem. Geol. Surv. 



Engl. Wales,' pp. vi, 91, Plate X. London, 1915. 

 Wethered, E. (1885). " On the Structure and Origin of Caiboniferous Coal Seams," 



' Journ. Roy. Micros. Soc.,' pp. 406-449, Plates VIII and IX. London, 1885. 

 White, D., and Thiessen, R. (1913). "The Origin of Coal: with a Chapter on the 



Formation of Peat," 'Bureau Mines Bull.,' vol. 38, pp. x, 304, Plate LIV. 



Washington, 1913. 



DESCRIPTION OF PLATES. 

 Plate 11 — The plain Plate. 

 Fig. 1. — Photograph of natural broken surface of durain. At right angles to the bedding 

 plane. Natural size. 



Fig. 2. — Photograph of natural broken surface of clarain. At right angles to the 

 bedding plane. Natural size. 



Fig. 3. — Photograph of natural broken surface of small block of banded clarain in the 

 centre of which is a broad definite band of vitrain. Note : In the photo- 

 graph, owing to its brilliantly refractive nature, the vitrain shows as a broad 

 white band. At right angles to the bedding plaiie. Natural size. 



Fig. 4. — Broken surface of vitrain showing irregular conchoidal fractures. This was 

 split parallel to the bedding plane. Natural size. 



Fig. 5. — Contact photo, made by placing A, durain, B, clarain, C, vitrain, on a negative 

 and enclosing them in a darkened chamber. Notice that the image obtained 

 thus directly from the various ingredients is much stronger from the vitrain 

 than from the others. 



Figs. 6, 7, and 8 are all of micro-photographs of the debris obtained by treating the 

 three ingredients by the method described on page 477. The three photographs are all 

 taken on the same scale of magnification and with the same time exposure. 

 Fig. 6. — Debris of fusain. Note the sharp angular shape and the solid black appearance 

 of the fragments. 



Fig. 7. — Debris of durain. Note the more polyhedral shape of the black fragments and 



the presence of a number of less opaque ones. 

 Fig. 8. — Dibris of clarain. Note the small number of black fragments and the high 



proportion of clear or nearly transparent fragments. Just above the centre 



several spores can be seen. Note also the much smaller size of the fragments 



from this material than from the other two. 



