267 
CALCAREOUS NODULES (‘ COAL BALLS ’) AND 
THEIR SIGNIFICANCE: 
R. CROOKALL, D.Sc., Ph.D. 
( Continued from page 256.) 
The * roof ’ nodules in Lancashire contain a greater 
proportion of land than of swamp-plants, though some swamp- 
plants are represented. The ‘ roof ’ nodules from the 
Yorkshire area, on the other hand, contain swamp-plants. 
It may be pointed out that the field of research provided 
by British ‘ coal balls ’ has been so thoroughly and expertly 
investigated by Williamson, Scott, Seward and others that, 
at the present time, new forms of plant are seldom found. 
It is only when fresh localities are discovered that any con- 
siderable proportion of new genera and species may be expected. 
It has been found that only about one per cent, of ‘ coal balls ’ 
sectioned from the old localities contains a plant structure 
of sufficient importance to warrant further sectioning. 
The following is a comparison of the botanical contents 
of f roof * nodules from Lancashire. 
‘ Floor ’ 
‘ Seam * 
‘ Roof ' 
Nodules. 
Nodules. 
Nodules. 
Swamp-Plants . 
(1) Clubmosses 
The only con- 
Very common 
Very rare 
S tig maria (roots 
tents of floor 
and rhizomes) 
nodules 
Lepidodendron 
— 
Very common 
Rare (and repre- 
(chiefly stems) 
sented by different 
species from those 
in ‘ seam ’ nodules) 
(2 ) Sphenophyllales 
— 
Common 
Absent 
(chiefly leafy stems) 
(3 ) Pteridosperms 
— 
Very common 
Leaves only 
(seed -ferns, chief- 
ly Lyginopteris — 
leafy stems) 
(4) Equisetales 
(‘ Horsetails * — 
- — - 
Common ( e.g . 
Very rare (and 
Calamites 
different species — 
chiefly leafy stems) 
communis ) 
e.g. C. ramosus) 
(5) Ferns 
— 
Common 
Absent 
(Botryopterids — 
chiefly stems and 
leaf -stalks) 
Land -Plants. 
(1) Pteridosperms 
— 
Rare 
Common 
(Seed -ferns — 
Medullosese — 
chiefly stems, 
leaves and seeds) 
(2) Gymnosperms 
— 
Rare 
Common 
(■ Cordaitales — 
chiefly stems, 
leaves and seeds) 
1933 Dec. 1 
