272 Calcareous Nodules (‘ Coal Balls') and Their Significance. 
possibly, as those of swamp plants) would be petrified in the 
accumulating sediments. 
In the second place, seams which contain ‘ coal balls ’ 
have clearly been affected by somewhat abnormal conditions. 
Deductions, drawn from such seams can be applied to coals 
which developed ‘ normally ’ only with caution. 
The writer 1 has expressed the opinion that the plant 
incrustations found in the immediate roofs of the majority of 
coal seams are substantially the same as those which compose 
the seams themselves. It is concluded, therefore, that the 
coal ball ’ flora of Lancashire does not vitiate the use of plant 
incrustations in stratigraphy. 
The Formation of Coal.— Professor E. C. Jeffrey admits 
that the strongest argument for the ‘ peat * or ‘ in situ ’ theory 
for the origin of coals appears to be furnished by ‘ coal balls.’ 
But he regards the debris which formed the coals containing 
* coal balls ’ as having accumulated by drift under water. 
On this point he observes that micro-sections of true peat- 
coals (which accumulated in situ but are regarded by him as 
very rare) show them to consist chiefly of disorganised wood. 
On the other hand, thin sections of ‘ maritime coals ’ (con- 
taining ' coal balls ’) show them to contain little wood and to 
consist chiefly of spores embedded in a dark matrix. (Such 
a dark matrix, composed of smaller decayed debris, occurs in 
both peat-coals and maritime coals). On this view the so- 
called ‘ maritime coals ’ resemble the cannels and bogheads 
(‘ lake -muck coals ’) and he considers that they were laid down 
like them, in open water. This is, of course, true of those 
relatively few seams which were deposited in definitely 
maritime waters. But most coals (even most of the coals 
containing ' coal balls ’) accumulated in Situ. 
The conclusion takes no account of those differences between 
coals which are usually ascribed to the differences between 
the biological putrifying agents (fungi and bacteria) and to 
differences in the periods during which they operated on the 
vegetable debris. Jeffrey, in fact, does not admit the import- 
ance of such activities in the process of coalihcation. On 
the other hand, he attributes coalihcation of the original 
vegetable debris solely to long continued heat and pressure. 
This, however, in the opinion of the writer, is negatived by 
the evidence obtained from the pebbles of coal which occur in 
Coal Measure sandstones — i.e. by the evidence from true 
‘ coal balls.’ Such pebbles of coal are of common occurrence 
in the sandstones of South Wales, Bristol and Somerset, 
known as the Pennant Rock, and the coal is uncrushed. It is 
evident that coalification was relatively rapid. The vegetable 
1 Crookall, R., ‘ The Lithology and Palaeobotany of Certain British 
Coals,' Fuel in Science and Practice, Vol. xii, 1933, p. 278. 
The Naturalist 
