1892-93.] H. B. Stocks on the Lower Coal Measures. 
69 
On certain Concretions from the Lower Coal Measures, 
and the Fossil Plants which they Contain. By 
H. B. Stocks, F.C.S. Communicated hy John Murray, 
LL.D. 
(Read May 1, 1893.) 
Coal, we are all aware, is a remnant of the organic matter of 
plants which flourished long ago. Owing to the length of time that 
has elapsed since the remains were entombed, and the pressure the 
material has been subjected to by overlying strata of great thickness, 
coal now presents to the unaided eye little or no evidence of organic 
structure, but is a lustrous black product not at all like wood in 
appearance. 
When thin sections of coal are examined microscopically, usually 
no trace of organic structure can be seen, but portions of plants, 
especially spore cases of lycopodiaceous origin, may be recognised in 
some specimens, the cells being considerably altered in appearance 
owing to the pressure and the chemical changes that have occurred 
in the deposits. 
Occurrence of Concretions in the Carboniferous Formations. — In 
the carboniferous system, concretions abound ; they are to be found 
in the millstone grit, in the coal, and in the accompanying shale. 
These concretions vary in appearance and composition according to 
the nature of the rock which encloses them ; in the present paper I 
shall deal with those that occur in the coal only. 
These particular concretions to which I refer occur in restricted 
areas, as at Halifax in Yorkshire and Oldham in Lancashire, the 
only two localities that I know of where these nodules are at 
present found. In these two districts they are known to the miners 
as “coal-balls,” from their shape and outward appearance. (See 
specimens exhibited.) 
Hot only do the coal-balls occur locally, but they are found only 
in one particular bed of coal, known as the “ hard-bed ” seam, 
belonging to the Lower Coal Measures or Gannister Beds. It is 
