Lake Tana is situated within the Tana Rift and owes its existence to a barrier of lavas south of the lake which is over 100 m thick (Mohr, 1962a). These lavas, which cover more than 3,000 km2, are principally basalts, basaltic breccias and tuffs and the more recent ones are associated with preserved cones and craters, which are especially numerous in the vicinity of Bahar Dar and Enjabara. Mohr (1962a) divides the lavas into six series five of which are essentially basalts. One series, however, called “silicic lavas” apparently includes rhyolites with sanidine and anorthoclase phenocrysts as well as nepheline-bearing rocks. Petrographic details are not given but amongst the 33 analyses reproduced there are ‘nepheline phonolites’ from Enjabara, nepheline trachytes from Amba Libo, sodic trachyte from Gashit as well as a range of rhyolites. Much of Mohr’s account is based on Comucci (1950), but I have not been able to obtain this reference.