STONE AGES OF CEYLON. 95 
In colour the newly cleft surfaces vary from almost black 
(rare) to white (also rare). The commonest colours are brown, 
greenish-brown (rarely distinctly green), various shades of 
buff, and an occasional gray. Brown chert, which is the 
commonest of all, is known to the Sinhalese as ginigala 
(fire-stone), and was in former days used by them, and also 
probably by the Portuguese, Dutch, and British, for gunflints. 
Dark red and pink shades are also to be found. 
Comparatively pure chalcedony also occurs, while in the 
North-Central Province (basin of the Kal-aru) common opal, 
due to the replacement of limestone by silica, has been 
occasionally made use of by early man; but the material is 
too soft to have been much sought after. 
The cherts are seldom homogeneous. The buff and brown 
varieties often contain strings and rosettes of a fibrous hghter- 
coloured silicious substance, in which the fibres are arranged 
at right angles to the length of the strings. Sometimes, too, 
the chert is brecciated or conglomeratic in structure, very 
rarely the latter. 
Under the microscope many specimens show a marked 
development of spheroidal structures, due to the segregation 
of the purer silica around numerous centres. The more 
ferruginous material lies between the centric structures. 
Some cherts, more particulary those of Uva, exhibit a finely 
mottled appearance; and in these the microscope reveals 
a system of branching, butt-ended rods or tubes. These 
strongly recall organic structures. I believe, however, that 
they are nothing of the sort. 
The origin of chert in Ceylon does not appear to be always 
the same. The mottled variety and that which contains the 
fibrous structures are formed, as far as my observations go, 
by the metasomatic replacement of gneissose and granulitic 
rocks by silica, a very curious and interesting phenomenon. 
Some grayish and brown cherts of the Northern Province 
appear to have been formed by a similar replacement of lime- 
stone. I say “appear” advisedly, for though I have never 
seen direct evidence of this replacement, I find it extremely 
difficult to account for the presence of the mineral otherwise. 
Some specimens from the extreme north of the Island bear 
