Canata is a ring structure with a diameter of 10 km. The ring is partly defined by an arcuate group of low hills with a central plain. The hills are principally composed of altered syenitic rocks and tuffs have been found in the northern part of the structure; petrographic descriptions of neither group have been traced. However, a nepheline-analcime syenite described from Monte Essale, presumably one of the ring of hills, by Andrade (1954) has a foyaitic texture and comprises alkali feldspar (44%), nepheline plus analcime (36.4%), aegirine and aegirine-augite (17.3%) and accessory titanite, apatite, cancrinite, natrolite and possible aenigmatite. A chemical analysis is given.