102 
Figs. 8 and 12 are specimens obtained by this method, 
and they show the layer formation to perfection, as many 
as fifteen layers being shown by one specimen. 
Fig. 12 is the end of Fig. 8, and it shows the concentricity 
of the layers very plainly. 
Fig. 0 is a small splinter, the centre of which was in a 
higher state of hydration than the exterior, so that when 
treated with hydrofluoric acid it left a hollow interior. The 
portion left shows the layers also. 
I noticed when rendering some of the opalescent rods 
transparent that they did not all show the same equally 
distributed transparency, but when viewed by transmitted 
light dark rounded patches of opaque matter appeared 
irregularly throughout the transparent portions, as shown 
by Fig. 3. When viewed by reflected light they showed 
themselves as white patches upon the opalescent ground, as 
in Fig. 10. It was found that by heating these rods in 
dilute caustic soda solution (about 2 per cent.) in sealed 
tubes to 130° C., the transparent portion could be dissolved 
away, leaving rounded nodules held together by a portion 
of the opalescent substance, which, viewed by reflected 
light, had the appearance given in Fig. 11. 
Dr. Young has figured in his paper, rods which are made up 
of nodules, and which present very much the same appearance 
as shown in the above figure if the whole of the opalescent 
portion were dissolved away, and it would appear as though 
they had been formed in somewhat the same way, that is 
by the solution of the more highly hydrated portions. The 
question is, how are the rounded nodules formed in the rods ? 
One of the largest I could find was carefully split and its 
structure examined, and it was seen when viewed under the 
microscope by reflected light to have the appearance pre- 
sented in Fig. 14, that is, it had the character of a radiating 
nodule of crystalline silica. 
Now it appears from the above evidence that in this case 
