Professor Harkness on Mineral Charcoal. 75 



the mineral charcoal, the coal having a bright aspect. In the 

 other coal, which is known under the name of the Creepy, we 

 have abundance of this substance, more particularly in the 

 higher part of the seam, which in some spots is absolutely 

 composed of mineral charcoal. The nature of the deposits 

 overlying this bed of coal points out from what circumstances 

 it derived its peculiar composition. The roof of the Creepy- 

 coal consists of a flaggy sandstone, such as would arise from 

 the operation of water in motion, in the form of currents ; and 

 previous to the deposition of this sandstone roof these currents 

 carried portions of plants, which became water-logged and fell 

 to the bottom, forming the mineral charcoal which enters so 

 largely into the composition of the Creepy coal. 



The occurrence of mineral charcoal is not confined to the 

 coal of the carboniferous formations alone. The oolitic coal of 

 Virginia also affords this matter, and the tertiary coals of Great 

 Britain, as these are developed at Bovey Tracy, also furnish 

 us with mineral charcoal. 



These, however, differ in their nature, and likewise in their 

 aspect, from those which are obtained from the true coal-fields 

 of Great Britain, yet there is every reason to conclude that 

 they originated from the same conditions. 



As regards the nature and origin of mineral charcoal, the 

 appearance which this substance presents at once furnishes 

 sufficient proof of its being vegetable matter. However, as it 

 has both a granular and a fibrous aspect, so it seems to differ 

 in its vegetable nature. When submitted to the microscope, 

 the granular variety does not afford the same regular struc- 

 ture as does the fibrous kind. The former appears to consist 

 of a mass of cells which are comparatively only slightly elon- 

 gated, and these have, so far as can be seen, the structure of 

 simple cellular tissue, which has probably been derived from 

 the ordinary plants usually entering into the composition of 

 coal. When this tissue is sufficiently hardened to admit of 

 its being sliced transversely, an arrangement of cells in a 

 hexagonal form is manifest, a description of tissue which 

 occurs in the woody cylinder of sigillaria as well as in the 

 gymnospermous vegetation which makes its appearance in the 

 carboniferous formation. 



Concerning the more fibrous variety of mineral charcoal, 



