Ingredients in Banded Bituminous Goal. 475 



inherently banded, as well as to have bands of fine durain intercalated 

 between its own bands (see Plate 11, fig. 2). 



VUrain occurs as definite rather narrow bands, in some instances straighter 

 and flatter than the other bands of coal, and in some instances more obviously 

 lenticular. True brilliant vitrain bands are often markedly uniform in 

 thickness for considerable distances, and are commonly from about 2 mm. to 

 3 or 4 up to 6 or 8 mm. thick, but are very seldom much more than 8 to 

 10 mm. thick. The limiting layer between the vitrain and the contiguous 

 clarain or durain is generally sharply marked and is often clean-cut definite 

 surface (see Plate 11, fig. 3). A single brilliant band does not exhibit the fine 

 banding detectable even in the brightest of clarain, but is a coherent and 

 uniform whole, brilliantly glossy, indeed vitreous, in its texture. The 

 compact vitreous band may split up readily in the fingers to small cube-like , 

 segments, but more generally they break irregularly when forced, as with a 

 penknife point, when the curved irregular faces have well-marked conchoidal \ 

 fracture (see Plate 11, fig. 4). As was mentioned in connection with fusain, 

 the contact-surfaces of vitrain with the other ingredients of coal tend 

 generally to be well defined with a firm, hard, and glassy face. 



Effects of the four Itigredients on the Photographic Plate. 



The four ingredients are differentiated by their potency in making images 

 of themselves directly (contact photos.) on sensitive plates. 



Small pieces of approximately pure durain, clarain, and vitrain were placed 

 on a negative, together with a little of the powdered fusain. All were taken 

 from one sample. 



By the method first described by Russell (of Eussell, 1906, 1908, and used 

 by Piatt and Wheeler, 1913), a contact photo, was obtained. 



The banded appearance of the contact photos, from blocks of ordinary 

 streaky coal has been observed by the previous workers ; the interest and 

 novelty of the present photo, (for which I am indebted to Dr. Wheeler) lies 

 in the very noticeable difference in intensity of the images made by the 

 vitrain and the other parts of the coal. This can be seen on Plate 11, fig. 5, 

 at A. That the brilliant vitrain should be the portion of the coal to make 

 the most intense image on the plate is a point the significance of which is 

 better discussed after some of the other characteristics of the four constituents 

 have been considered. 



Behaviour of the four Ingredients with certain Chemicals. 



Work with a variety of chemicals is being undertaken, but the present 

 paper is intended mainly to lead up to the microscopic distinctions between 



