Anvil Island is underlain by Lower Cretaceous Gambier Group volcano-sedimentary rocks. At the Anvil Island occurrence at the extreme south end of the island, there are extensive deposits of Recent stratified glacial clay, probably related to the Puyallup Interglacial deposits described on Vancouver Island. Two deposits have been historically worked. The clay bank has an area of 36 hectares and a thickness of approximately 30 metres. The clay in these deposits is somewhat sandy and yellowish to bluish-grey in colour and in most places contains fairly abundant pebbles. A sample from an old operation (Columbia Clay Company) is described from Bulletin 30 as follows:

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Clay: Upper yellowish-grey

Workability: Good plasticity

Drying: Fairly good, slight cracking at 80 degrees Celsius

Firing characteristics:

Cone Shrinkage Absorption Remarks

(per cent) (per cent)

010 0.35 16.74 Light red,

fairly hard.

03 3.10 7.76 Good red,

very hard.

1 Fused

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Analytical results of the clay in 1906 were: 58.6 per cent silica, 26.7 per cent alumina, 7.5 per cent iron oxide, 4.0 per cent lime, 3.0 per cent loss by ignition, trace magnesia and a fusion point of 1093 degrees Celsius (Minister of Mines Annual Report 1906).

Production of clay for use as common brick from the two operations (Columbia Clay Company and Anvil Island Brick Company, Ltd.) dates from 1897 up to late 1912 but no production figures are available.