192 REINHARDT THIESSEN 



Figure 9 is a random horizontal section of coal from the same bed 

 showing that woody structure is present everywhere. 



The illustrations given represent the average conditions of most 

 coals in which it is not difficult to detect, in any cross-section, 

 plant structures in most of the strips in question. In some coals, 

 like that from the Vandalia mine and that from Buxton, Iowa, 

 it is not so easy to detect structures so readily in cross-sections. 

 In the horizontal sections, however, plant structures are invariably 

 revealed. 



The coal from the VandaKa mine near Terre Haute, Indiana, 

 as shown in Figure 10, at a low magnification is compiled of innum- 

 erable thin strips separated by very thin layers of attritus. Cross- 

 sections, at a higher magnification, are shown in Figure 11. The 

 bands a-i, a-3, and a-5 represent some of the thin strips seen in 

 Figure 10. There is very little in these that resembles plant 

 structure. In the horizontal sections, on the contrary, no matter 

 where cut, it is clearly shown that these strips still bear a pro- 

 fusion of plant structure as seen in Figure 12. Of all the coals 

 examined the Vandalia coals contain the poorest preserved struc- 

 tures. Similarly in all coals there are many strips in which at a 

 casual observation no or little direct plant structure is noted, 

 but when such specimens are examined in horizontal sections, plant 

 structure is invariably found to be present. There is, nevertheless 

 direct evidence of such structure almost always observable in 

 cross-sections in the great majority of strips. It will be noticed 

 that most of them have a finely striated or fibrous appearance 

 and th^'s structure is due to the remaining plant structure in the 

 strips. This structure becomes recognizable in the horizontal 

 sections and hence is a direct evidence of cell structure. 



A large number of horizontal sections have been prepared from 

 a considerable number of coal seams and in every case cell structure 

 still existed in these thin laminae. The evidence may be con- 

 sidered conclusive. 



There exists, therefore, little doubt that the thin bands of bright 

 coal forming a large part, and in many the largest part of the dull 

 coal of ordinary bituminous coals, are also derived from the woody 

 parts of plants. But instead of representing larger parts of plants 



