Vegetation of the First Period of an Ancient World. 1 1 3 



explanation. Some years ago a friend of mine found a kettle bot- 

 tom at Old Kenton colliery, eighteen inches in diameter, coated with 

 fine coal, the substance of which was entirely mineral carbon, or 

 charcoal, with a mixture of earthy matter and pyrites. A portion 

 of this specimen is in the collection of the Geological Society. 



It is much to be regretted that hitherto none of these interesting 

 fossils have been followed into the strata. We do not know how far 

 they extend, or to what height they are standing. 



Again, in the coal districts of Scotland, amongst the troubles which 

 affect the roofs of coal, there is one of a very singular form, known 

 by the name of pot bottom or, cauldron bottom, and are from the size 

 of a foot to five feet in diameter. One of these is represented in 

 the annexed diagram : 



a. Roof of Coal. Argil with sand. 



b. Pot or Cauldron bottom. 



c. Coal bituminous. 



d. Pavement of Coal. Fire Clay. 



In working the bed of coal, the miner generally knows that he is 

 approaching one of these, by the coal becoming twisted, and more 

 difficult to work, and this continues till this trouble in the roof is pass- 

 ed. The general form is that represented in the figure, when, of 

 course, the mouth of the pot is always inverted. The sides of it 

 are generally lined with coal from one-eight of an inch to an inch in 

 thickness, and the pot or cavity is filled up with stone of the argilla- 

 cious kind, or fire clay, having generally less mixture of sand than 

 is in the roof stone around. The under surface of the stone which 

 fills the pot is irregular and waving, not smooth like the roof adjoin- 

 ing. Although the coal which lines the pot is connected with the 

 main bed of coal, it is of a texture altogether different, having a bright 

 appearance like jet, and breaks into very minute cubical pieces. 

 Sometimes it has no bitumen in it, and is of the nature of glance 

 coal. The sides of the pot are generally as smooth as glass, with 

 small furrows or grooves in a vertical direction, so that there is very 



Vol. XVIII.— No. 1. 15 



