Lying on the intersection of the east-west-trending Mexican Volcanic Belt, which is predominantly andesitic, and the essentially north-south-trending eastern, or oriental, alkaline province, the Palma Sola complex includes both calc-alkaline and alkaline rock suites (Robin, 1982, p. 21). The earlier Miocene calc-alkaline rocks are essentially adnesites and their intrusive equivalents. The later alkaline series dconsists predominantly of Pliocene to Recent alkaline olivine basalts amongst which, particularly in the small cones of La Cruz and El Abra, are basaltic rocks containing modal nepheline and analcime. Some of these are referred to as nephelinites by Robin (1982, p. 24) but they contain plagioclase and an analysed specimen (op. cit., p. 460, no. VE 67) has 25% normative feldspar and 21% nepheliine.