A volcanic field comprising basalt, rhyolite and trachyte and extending for 30 km in a northeasterly-southwesterly direction is shown on the 1:500,000 geological map (Besairie, 1971b). No details of the petrography of these rocks have, however, been traced.
BESAIRIE, H. 1971b. Carte Géologique. Feuille 2. Antalaha. 1:500,000. Service Géologique de Madagasikara, Tananarive.