TRANSACTIONS OF SECTION C. 487 
Among the numerous fossil fragments that occur in the Lower Cambrian 
Limestones of this excavation the following have been identified :— 
Anomocare (?) pustulatum Cobbold, Callavia Callavei Lapworth (?) Micro- 
discus Attleborensis 8. and F. sp., Protolenus sp., Kutorgina sp., Linnars- 
sonia (?) sp. 
Excavation No. 55 exhibits a faulted junction between the Middle and Lower 
Cambrian, the hard, ringing Grit (beds d above) being brought into contact 
with the Green, Micaceous Sandstone (beds a above). 
Excavation No. 56 proved the existence of both the Quartzite and the lower 
part of the Lower Comley Sandstone at another point in the area. 
A section constructed embodying the results of these excavations provides 
evidence that the Lower Comley Sandstone has a thickness of about 480 feet. 
The paper was accompanied by a sketch-plan showing the exact positions 
of the excavations, and a section through the Comley and Cwms areas indicating 
the general relations of the deposits to one another and to the superincumbent 
younger rocks. 
5. Flint and its Genesis. By A. Irvine, D.Sc., B.A. 
A. Inthology of Flint. 
1. Flint, intrinsically a member of the family of minerals’ having the com- 
mon characteristic (as compact minerals) of consisting essentially of silica (SiO,) 
with slight traces of accessory ingredients (commonly iron and carbonaceous 
matter, more rarely potash, alumina, and lime), has closer affinities with 
chalcedony, opal, menilite (retinite), holding a certain amount of water in 
combination, as distinct from mechanically contained water. (Fuchs, Bischoff, 
Rammelsberg, Wislicenus referred to.) 
2. Iron staining referred to well-known chemical sequence? of (i) dissolved 
protosalts of iron penetrating the flint differentially according to molecular 
structure; (ii) the peroxidation of the iron base with the breaking up of the acid 
constituent of the salt on the access of free oxygen, more fully discussed by the 
writer elsewhere. Reference to the excessive iron-staining of the Sussex flints 
(Piltdown) as a demonstration of this in Nature’s laboratory. 
3. Patination of fracture-surfaces considered as an incipient stage of devitri- 
fication, involving the metatropic change from the vitreous to the stony or 
porcellanous molecular structure of the mineral.’ : 
Evidence forthcoming of the action of heat and sunlight under desert con- 
ditions in promoting devitrification (quad crystallisation) ; ‘Réaumur’s porcelain’ 
referred to again; also the lithological change observed in flaked flints brought 
from the Egyptian desert.* Accessory minerals in the flint important factors 
of devitrification. Work of Stas> on the action of acids upon different kinds of 
glass; action of humus-acids on glass buried for a Jong time in the soil; forma- 
tion of crystalline masses (richer in lime and magnesia‘) in glass during the 
incipient stage of congelation—all throw light on this occult question. Refer- 
ence to ‘ Report on Diffusion in Solids’ by Dr. C. H. Desch (in the last Report 
of the British Association, Dundee Meeting, 1912), ‘diffusion in glasses and 
devitrification.” Any attempt to classify flints according to age by mere ‘ patina- 
tion’ or iron-staining, regardless of (a) the variations in secondary character 
of the flints, (6) the physical conditions to which they may have been exposed 
at different periods of their history, appears to be in the highest degree empirical. 
4. Htching is referred to unequal responsiveness to the action of natural 
* Kalkowsky, Hlemente der Lithologie (xviii., Familie der Kieselgesteine). 
2 A. Irving, (a) Brit. Assoc. Reports, Southport Meeting (1883), Sect. C; 
(6) Proc. Geol. Assoc. vol. xii. pp. 227 ff.— Organic Matter as a Geological 
Agent.’ 
* A. Irving, Chem. and Phys. Studies in Metamorphism (Longmans, 1889), 
§ iii., and App. i. 
* Presented to the writer at the time by Captain H. G. Lyons, R.E., F.R.S. 
5 Percy, Metallurgy (vol. i.) quoted by the writer (op. cit.). 
* Percy, op. cit. 
