CASH & HICK: FLORA OF THE LOWER COAL MEASURES. 75 
PHYSICAL CONDITIONS. 
The fossil plant remains showing structure are in this 
district, so far as our knowledge and experience goes, entirely 
restricted to the Halifax Hard Seam. This bed consists of 
an earthy coal of very inferior quality, which in many parts 
is so thickly studded with nodules, varying in size from that 
of a nut to that of a man's head, or larger, as to render it 
unworkable. These " coal balls," as the nodules are locally 
called, are composed chiefly of carbonate of lime ; and when 
broken up are found to contain stems, rootlets, and branch- 
lets of plants, and sometimes cones, spores, and other organs 
of fructification are found. It is to be remarked that these 
nodules are not evenly distributed through the seam, but 
occur in large groups, whilst considerable areas are free from 
them. The average thickness of the " Halifax Hard Coal 
Bed " is about two feet. The roof consists of a thin stratum 
of black shale, some four inches or so thick, and this is often 
composed almost entirely of the flattened valves of what is 
accepted as a marine bivalve mollusc, the Aviculopecten 
papyraceus, Gold. Above this thin layer is a bed of shale, 
averaging a thickness of about five feet, and in this bed are 
numerous calcareous nodules, often coated over or even im- 
pregnated with iron pyrites. These are locally known as 
" brass lumps" and "baumpots," and when broken up are 
found to contain fossils, sometimes of vegetable origin, some- 
times fish remains, but most commonly shells of the marine 
genera Aviculopecten, Posidonia, Orthoceras, Goniatites> 
Nautilus, &c, &c. — a characteristic shell being Goniatites 
Listeri. At the base of the coal seam is found a hard, com- 
pact fireclay, known as Ganister. It is penetrated in various 
directions with the roots and rootlets (Stigmaria) of the 
plants which once grew upon it, and whose compressed and 
altered remains constitute the mass of the immediately 
overlying coal. 
