464 



THE CARBONIFEROUS SYSTEM. 



fracture, — or of coarse coal, containing much earthy matter. All 

 of these are arranged in thin interrupted laminae. They consist of 



Fig. 175. — Tissues from Coal. 



(a) Tissues of axis of Sigillaria. (b) Tissues of Calamites? 



(c) Tissues of Ferns. (d) Scalariform vessel of Lepidodendron. 



vegetable matter which has not been altered by subaerial decay, but 

 which has undergone the bituminous putrefaction, and has thereby 

 been resolved into a nearly homogeneous mass, which still, however, 

 retains traces of structure and of the forms of the individual flattened 

 plants composing it. As these last are sometimes more distinct than 

 the minute structures, and are necessaiy for their comprehension, I 

 shall, under the following heads, notice both as I have observed them 

 in the coals in question : — 



1. The laminae of pitch or chei'ry coal, when carefully traced over 

 the surfaces of accumulation, are found to present the outlines of 

 flattened trunks. This is also true, to a certain extent, of the finer 

 varieties of slate coal ; but the coarse coal appears to consist of exten- 

 sive lamina? of disintegrated vegetable matter mixed with mud. 



2. When the coal (especially the more shaly varieties) is held 

 obliquely under a strong light, in the manner recommended by 

 Goeppert, the surfaces of the laminaa present the forms of many 

 well-known coal-plants, as Sigillaria, iStigmaria, Cordaites, Lepido- 

 dendron, Lepidophloios, and rough bark, perhaps of conifers. 



3. When the coal is traced upward into the roof- shales, we often 

 find the laminae of compact coal represented by flattened coaly trunks 

 and leaves, now rendered distinct by being separated by clay. 



4. In these flattened trunks it is the outer cortical layer that alone 

 constitutes the coal. This is veiy manifest when the upper and under 



