In the Kilchrist vent on Skye, off the west coast of Scotland, acid intrusions are emplaced in the basaltic agglomerate. In the eastern marginal mass, a felsite occurs between the inner margin of a microadamellite and the vent agglomerate which is a tuff consisting primarily of fragments of basic lavas. Field and petrographic relations are reported. Laminar structure in the tuff matrix and other evidence indicate that the assemblage of fragments acted in a manner similar to fluid injection. Veinlets of tuff are found penetrating a xenolith within the tuff. There is a gradational relationship between the felsite tuff and the felsite, with the laminar structure disappearing as a microgranular texture appears. It is assumed that the felsite tuff grades into the felsite, metasomatized in place.