100 SPOLIA ZEYLANICA. 
Before passing on to speak of the geology of the plateau 
deposits and their derivatives, I must say a word upon the 
much-discussed subject of patination. By patination is meant 
the surface changes affecting the colour and other physical 
characters of flint or chert. Crystal quartz is not liable to 
these, but may become frosted either by constant collision 
with other stones and particles of sand in motion, as in a river 
bed, or by long-continued exposure to the influence of the 
weather. In the former case the surface of the stone is 
generally covered with a meshwork of microscopic cracks ; 
in the latter, the surface resembles that of ground glass, but 
is infinitely finer. 
Patination is a big subject, but I shall dismiss it briefly. 
Some chert tools acquire during the course of ages a deep 
almost black hue, others affect ochreous shades, and a good 
many of them turn white of these only Ishallspeak. Ceylon 
chert is an intermediate mixture of crystalline and colloid 
silica. The first is hardly soluble at all, the latter is more 
easily dissolved in alkaline solutions. Consequently the 
colloid particles are leached out during the course of centuries, 
and what remains is nothing but a spongy mass of tiny 
erystals which reflect the light, much as powdered chert would 
do, and make the stone look white. 
The degree of rigidity of the spongy matter depends, of 
course, upon the ratio of the colloid to the crystalline material 
in the original chert and the proportion of the former removed. 
It would appear that the cherts of this country contain a high 
percentage of uncrystalline material, with the result that they 
are far less stable than European flint, which contains less, 
Indeed, not a few tools and flakes which I have collected are 
so “‘ rotten” that one can scrape their surfaces with as much 
ease as one could a piece of chalk. 
In certain circumstances fresh silica, drawn up probably 
from the as yet undecomposed chert below the surface of a tool 
by a process akin to inflorescence, is apparently deposited in 
crystalline continuity with the surface grains ; and, as a con- 
sequence of this, the tool presents a glazed exterior. The thin 
crust thus formed is tolerably resistant, and protects the 
‘rotten ’’ layer below, which is generally so porous, that it 
