SECTIONAL TRANSACTIONS.—C. 481 
good evidence that particular coal seams are characterised, over a wide area, 
by an assemblage of certain groups of microspores present in fairly definite 
proportions. ‘The principal microspore types are illustrated and described. 
Prof. G. Hickiine and Mr. C. E. MarsHaLi.—Recent studies of plant 
structure in coal (10.35). 
Improvements in the technique of section-cutting and photography have 
made it possible to show that coal consists largely of plant-remains in which 
the details of the original structure are preserved with remarkable perfection. 
This detail, in some respects, far exceeds that which can be observed in the 
familiar calcified or silicified petrifactions or coal-balls, since in the coal most 
of the original substance of the plant remains, while in the petrifaction it has 
been replaced. By the study of isolated sheets of bark and portions of wood 
which are preserved as coal in the coal-measure shales the microstructure 
of the plants can be studied in relation to their external form. ‘The bark- 
structures of Lepidodendron, Bothrodendron and Sigillaria have been so 
studied, as well as certain woods. In certain cases it appears possible to 
demonstrate conclusively that the existing coal consists in part of the original 
plant-substance and in part of additional organic material which has been 
absorbed by the plant after death. 
Mr. A. T. J. DoLLaR.—The dike-swarm of Lundy (11.30). 
The Lundy dike-swarm comprises 122 dominantly vertical rock-sheets 
of basic and intermediate composition which occur respectively in the pro- 
portion of 91:9. It includes typical crinanites, olivine- and analcite- 
dolerites, quartz-dolerites and tholeiites, together with orthophyres, vitreous 
and non-vitreous andesites and pitchstones. Extreme types are repre- 
sented by metallic ores, gabbroid rocks and very vitreous pitchstones. The 
assemblage as a whole is distinctly Tertiary in affinity. 
These dikes cut both the coarse granites and Devonian sediments of the 
island with an average frequency of 26 per linear mile of coast. The mean 
thickness of an individual sheet is about 4 ft., but the basic varieties range 
between 3 in. and over 20 ft., while the less abundant types of inter- 
mediate composition generally exceed 10 ft. in breadth. The width of the 
swarm is approximately coincident with the north-south length of the island, 
and a crustal extension of 3 per cent. has been produced in this direction 
by the minor injections. 
Apart from intermediate and basic intrusions there are numerous thick 
and thin inclined sheets of microgranite which are confined to the major 
granites of the island, while many quartz veins cut both the granites and 
sediments. The two kinds of microgranites are remarkable for their 
similarity to granophyric rocks of the Mourne Mountains, Ireland. 
The distribution of intermediate and basic dikes is rigidly controlled by 
jointing and fan-fractures. The latter radiate from centres which appear 
to lie on submarine planes of weakness. Magnetic properties of the basic 
dikes have been investigated and are comparable with those of corresponding 
British Tertiary rocks. 
Dr. FREDERICK WALKER.—The Crinanite dike of Maiden Island, Oban 
(11.45). 
The bulk of Maiden Island (about 13 miles north-north-west of Oban) 
consists of a north-north-west crinanite dike of great breadth and con- 
siderable diversity of composition. The west contact of the dike is not 
