In the vicinity of Arusha and Monduli nearly 100 small craters, tuff cones and tuff rings have been mapped (Dawson, 1964a and b; Dawson and Pickering, 1964; Dawson et al., 1970; Wilkinson et al., 1983). They are rarely more than 200 m in height and up to 3 km in diameter, though many are a kilometre or less across. They are built principally of welded scoria and lapilli but carbonate-rich pyroclastic rocks are a major component of some. The scoria is generally basaltic in composition but may contain a little nepheline. A number of cones are very rich in a variety of xenoliths including many very fresh ones of mantle origin. Lashaine is a small volcano a little over 200 m high south of Monduli (Dawson, 1964a). A crater is surrounded by a ring of red, welded, olivine-phyric ankaramite scoria which is overlain by calcite-rich tuffs and agglomerates. The latter rocks comprise up to 70% calcite rich in Sr, Ba and La, and include blocks of olivine basalt, red scoria, gneiss, granulite and ultrabasic rocks, the last of which are rarely greater than 30 cm in diameter, most being much smaller. The ultrabasic xenoliths include garnet and spinel peridotites, harzburgite, websterite and dunite and numerous papers have been published describing them including Dawson et al. (1970), Dawson and Smith (1973), Reid et al (1975b), Rhodes and Dawson (1975), Ridley and Dawson (1975), Pike et al. (1980) and Henjes-Kunst and Altherr (1992); granulite xenoliths are described by Jones et al. (1982a). Data on He and Sr isotopes in xenoliths will be found in Porcelli et al. (1986), and of Pb, Nd and Sr isotopes and U, Pb, Sm, Nd, Rb and Sr concentrations in Cohen et al. (1984), while Hutchison and Dawson (1970) give Rb, Sr and 87Sr/86Sr isotope data for xenoliths and host rocks. Harzburgite, clinopyroxene dunite and wehrlite xenoliths containing glass have been described from the Olmani cone 8 km southeast of Arusha (Jones et al., 1983). They are well rounded, up to 30 cm across, and set in ankaramitic agglutinate. Peridotites are described by Jones et al. (1982b) and Rudnick et al. (1993), the latter paper, in particular, including a very full set of major and chemical element data. Brief descriptions of the Lemagur and Loljoro tuff rings and Cameron's Crater are given by Dawson (1964a). The tuff rings are of basaltic fragments with a thin outer layer of calcite-rich tuffs at Lemagur and a calcite matrix to the pyroclastics at Loljoro. Cameron's Crater is a 1 km diameter maar of agglomerates and breccias cemented by calcite. The small conical hills of Mutelelu and Loiwilokwin consist of calcite tuffs containing blocks of basalt and fragments of orthopyroxene.