480 



Dr. M. 0. Stopes. On the Four Visible 



granules. These, though sometimes locally abundant, are less characteristic 

 of durain than of clarain. One may say that, on the whole, durain is 

 essentially composed of a high proportion of opaque, fine granules, with many 

 macro- and microspore exines scattered through it like currants in a pre-^war 

 pudding. Even in a small streak of durain the spore exines tend to be 

 flattened and oriented so as to lie parallel to the general bedding of the coal 

 seam. 



The clcvrain is the easiest portion of the coal to cut into good sections,' and 

 is the most interesting to the paleeobotanist, for in the clarain lie the 

 greatest variety of recognisable plant tissues and structures. Clarain is 

 essentially clear, as contrasted with the opacity of durain. There may. be in 

 it clear bands and zones showing much disintegrated plant substance, also 

 bands of clear cuticle, spore exines, " resin-bodies," and other structures of 

 various shades from pale yellow to a rich reddish-amber, the great majority 

 of which are translucent or semi-translucent (though among them may be 

 some opaque granules and particles), and among this variety of material 

 plant stem tissues, leaf-tissues and so on may be preserved and may even fill 

 the whole area of the sections. Plant tissues so preserved are also essentially 

 transli;cent, though colour contrasts of the various minute structures present 

 make the cellular tissue evident. There are also, of course (see p. 475), the 

 opaque streaks of durain which are common in clarain, and should be looked 

 on ds an impurity in it. As a general rule, one may say of clarain that it is 

 essentially translucent in thin section, and the purer the clarain the more 

 are all its components of some degree of translucency [see Plate 12, fig. 3 

 (coloured)]. Even in a small area of clarain, that forming a fine bright 

 streak in a dull piece of durain, for instance, the arrangements of the 

 materials in it tends to be parallel to the general bedding of the coal seam. 

 Comparison of a number of sections with the various published illustrations 

 makes it clear that clarain is the happy hunting ground of the palaeonto- 

 logist in search of preserved remains of the tissues composing coal, and 

 fortunate it is for him that so large a proportion of most ordinary seams are 

 more or less pure clarain. In it remains of all kinds are to be found, 

 ranging from very small fragments up to preserved stem tissues running for 

 inches unbroken in the coal. It appears that the richer detail and variety of 

 structures in the clarain, more or less pure, have attracted most recent 

 workers, and have formed the basis of the great majority of the good illustra- 

 tions hitherto published on the micro-structures in coal. 



Vitrain is, in my experience, unobtainable pure in large sections, as true 

 vitrain occurs almost entirely in thin bands, which tend to break into small 

 segments. In section, when pure, its essential characters are its translucency 



