C.—GEOLOGY 49 
of these smaller cells.’ He notes the frequent interbanding of these 
different types of coal, and acutely observes that since they occur together 
(sometimes in bands “ as fine as a hair ’) their differences must be original, 
and cannot be due to any changes subsequent to their entombment. He 
notes especially, the occurrence of ‘ charcoal’ intimately mixed with 
‘the most splendent’ coal as evidence of the fact that the former must 
have been in the condition of charcoal at the time of its enclosure. The 
observation that the coating of some of the larger fossil plants enclosed 
among the shales is ‘ converted into the finest and most crystalline coal’ 
is noted as evidence that entombment among other plant material is not 
necessary for its conversion into this type of coal. His final conclusion 
is ‘ that every variety of coal is of vegetable origin,’ and ‘ the difference 
of the nature of these varieties has most probably arisen from an original 
difference in the nature of the vegetables of which they were composed.’ 
Hutton had clearly recognised that bright coal consists almost entirely 
of translucent and apparently homogeneous material in which plant 
structures are discernible here and there; that some dull coal is largely 
composed of megaspores and microspores (the true nature of which 
he could not know); and that these types of coal are often finely inter- 
banded, together with layers of mineral charcoal. This was the first 
serious attempt to determine the structures of the different kinds of coal, 
and little advance was made in this matter for over half a century. 
During this long period, advance was due to the slow accumulation of 
isolated observations rather than to any sustained effort to study coal 
itself as a major problem. The difficulty of preparing satisfactory sections 
obviously discouraged most workers from serious attempts in that direction, 
while those who made such attempts lacked some of the knowledge to 
interpret what they saw. By the use of bleaching and macerating agents 
many observers were able to show that such minute details of plant- 
structure as the fine pittings on the walls of wood-fibres were perfectly 
preserved, spores and cuticles were isolated from the coal, and even traces 
of the softer tissues of the plants were found. But it would seem that 
almost all workers throughout this period looked upon the fragmentary 
plant remains merely as interesting indications of the material out of 
which the coal had been made. It appears to have been usually taken 
for granted that such remains were merely items in the mass of the coal, 
a great part of which was assumed to bestructureless. It was not expected 
that most of the plant material would have retained any trace of its 
original organisation. ‘The surprise, therefore, of the modern work, is 
the discovery that in the more common types of coal, at least, nearly every 
portion of the mass can be seen to retain evidence of its orginal organic 
structure. 
Recent Work.—The modern period of coal petrology is clearly the off- 
spring of the palzobotanical research on petrified coal which culminated at 
the close of the nineteenth century. This work gave us a precise know- 
ledge of the structure of the plants which formed the Carboniferous coals, 
and a clear picture of the condition of some of the coal peats at the time of 
their deposition. It was inevitable that this should be followed by more 
determined attempts to see these structures in the coal itself, and was 
