204 REINHARDT THIESSEN 



but a small part of any coal, but they are much talked about on 

 account of their conspicuousness and prominence in the mineral 

 charcoal and on the cleavage surfaces. They are called rodlets 

 because they have the appearance of minute rods. By some they 

 are also called needles, because of their slender needle-like appear- 

 ance. In cross-section, the rodlets appear as circular to oval 

 disks of a dark color in very thin sections; in thicker sections 

 they are opaque. They are of a relatively large size when com- 

 pared with spores and pollen grains. 



Many of the rodlets are scattered helter-skelter through the 

 attritus (Fig. 43). In some laminae they are present in large 

 numbers, and in such cases, form a large proportion of the coal. 

 Many of the anthraxylon components (Fig. 44) , and, conspicuously, 

 many of the mineral charcoal constituents, inclose many rodlets 

 that are evidently part of their structure or tissue. Some of the 

 tissues in coal with which rodlets are associated may be classified 

 with the Medullosae (Fig. 44), well-known Paleozoic plants 

 allied to the Gymnosperms. The cortex of the Medullosae is 

 known to have been pervaded by gum or mucilage canals. In a 

 specimen at hand of Medulosa Anglica (Fig. 42), these canals are 

 still filled with a "dark solid substance. These solids resemble 

 very closely certain rodlets embedded in the attritus, as well as 

 those associated with anthraxylon components. 



The rodlets are non-resinous, give off a blue non-sooty smoke 

 on burning, do not swell or puff up, and do not become viscous when 

 heated. They are of a black, glistening, glassy consistency, break- 

 ing with a decided concoidal fracture. When burned, they leave a 

 very delicate, finely grained skeleton of quarts, the relative amount 

 of which varies very largely in different rodlets. In some it forms a 

 very delicate skeleton, while in others there remains a solid mass 

 almost as compact as was the rodlet before burning, except that it 

 is now snowy white. Between these two extremes, all possible 

 intergrades may be observed. In fact, some rodlets consist of 

 almost pure white quartz. Some have a core of quartz surrounded 

 by a shell of black matter. 



It seems clear then that some of the rodlets, if not all, are the 

 semi-petrified or petrified contents of the mucilage canals of certain 

 Cycadofi.licales, like Medullosa, 



