Within Eocene volcanic rocks on the eastern margin of the Chilcotin Plateau are glassy volcanic flows in which the glass, both in hand specimen and thin section, has characteristics of perlite. These rocks are probably equivalent to the Eocene Kamloops Group to the east of the Fraser River.

Whereas most of the occurrences of volcanic glass do not expand upon heating and, hence, are not strictly perlite, the French Bar Creek showing contains about 9 per cent water and upon heating expands to about 50 per cent of the perlite mined by Aurun Mines near Empire Valley. The French Bar Creek showing is a single large outcrop of porphyritic flow banded dacite.