Zeolite facies assemblages are described in lower Tertiary volcanic graywackes (grès de Taveyanne) of the Thônes syncline (Haute-Savoie, France). In the northeastern part of the syncline laumontite is found, whereas heulandite takes its place near the southwestern extremity. There is thus a decrease in metamorphism in a southwesterly direction with the transition from metamorphic to diagenetic conditions. This is probably related to a decrease in the thickness of the overburden (prealpine nappes). The zeolite minerals are found not only as rock constituents but also in sheared zones and in fissures. The sheared zones mineral assemblages indicate a slightly more intense metamorphism than the associations of minerals found in the rock.