162 A. LIVERSIDGE, 
- concentric structure, might have been deposited either 
upon a nucleus of, or upon the interior walls of a cavity, in 
the same way that agates have been formed by the depo- 
sition of silica and chalcedony. Wrom the way in which 
the contour lines at a and Db run parallel with the sharp 
angle at ¢ (Plate 12) and then suddenly flatten out to the 
left, renders it [ think, unlikely that the nugget was built 
up about a nucleus, but it is easy to understand that the 
layers may have followed the irregularities of a cavity. 
The more central parts do not show any lines of deposition. 
It is also noticeable that these two nuggets do not in 
any part show any undoubted crystalline structure; when 
examined under the higher powers, (in Plate 13 the enlarge- 
ment is 50 diameters) they, on the contrary, present a 
somewhat spongy or cellular appearance, although the 
portions which look like cavities are really solid; the gold 
in these parts may have been deposited in a spongy or 
cellular form, and the interstitial spaces afterwards filled 
in. The photographs are taken from the smaller nugget, 
the larger one shows the concentric structure much less 
well marked and is hardly traceable. 
