Figs 61 and 62The Crater Hills extend over an area of approximately 80x70 km, immediately to the northeast of Uweinat (No.049-00-048), and include those known as 'Peter' and 'Paul'. They comprise about 18 plugs of basalt, trachyte, quartz trachyte and rhyolite with some phonolite. The trachytes contain aegirine and a sodic amphibole, which may comprise as much as a third of the rock, and up to 9% modal nepheline (Bishady and El Ramly, 1982); biotite is sometimes abundant. One intrusion is described as consisting of alkali rhyolite but alkali pyroxene or amphibole does not appear to be present. Modal and chemical data, including some trace elements, are available (Bishady and El Ramly, 1982).