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Heulandite occurs with stilbite and other zeolites in the amygdaloidal cavities of basaltic volcanic rocks, and occasionally in gneiss and metalliferous veins.

Its original repository appears to have been the volcanic and amygdaloidal rocks about its sources, which have been extensively broken down by geological mutations, during ante-historical periods.

Occasionally we meet with igneous rocks which are more or less vesicular and amygdaloidal throughout their entire mass.

Apophyllite is a mineral of secondary origin, commonly occurring, in association with other zeolites, in amygdaloidal cavities in basalt and melaphyre.

The only rocks noticed when we crossed these hills on the late journey, were clay-slate, greenstone, and dark red sandstone, sometimes containing white calcareous concretions, resembling an amygdaloidal rock.