Proc. Roy. Socy. of Edin. ] 
[Vol. XXX. 
Fig. 3. — A section across the Glenboig fireclay, of a 
sample unusually rich in iron, and showing the 
bedding and large quartz grains. xlO diameters 
(ordinary light). 
Fig. 4.— Section across Glenboig fireclay, showing the 
bedding and occasional vertical flakes of quartz, 
x 30 diameters (ordinary light). 
Fig. 1. — A thin section of the Glenboig fireclay, 
showing a layer with many crystals of sidero- 
plesite. x 30 diameters (ordinary light). 
Fig. 2. — One of the same crystals, x 66 diameters 
(ordinary light). 
J. Fingland, Phot.] 
