These are conformably overlain by peperite and the basaltic and andesitic Lorne plateau lavas. The lower flanks consist of mostly basaltic and some andesitic lavas. Block lava flows are typical of andesitic lavas from stratovolcanoes. The Mongolian Plateau has an area of basaltic lavas and volcanic cones. Eruptions of rhyolite are relatively rare compared to eruptions of less felsic lavas. Both andesitic lavas and tuffs (volcanic ashes) are represented. This may have formed from contractional cooling of basaltic lavas. Within the Deccan Traps at least 95% of the lavas are tholeiitic basalts. Major eruptive pulses of flood basalt lavas are laid down stratigraphically. The island is mainly composed of the Jurassic Lemaire Formation, composed of tuffs and lavas. Another member of the expedition later described "cellular basaltic lavas" at the mountain's base. It consists of largely intermediate composition lavas and breccias. The Quaternary lavas are directly on the Jurassic sediments. For volcanic rocks, mineralogy is important in classifying and naming lavas. The lavas are intersected by post-shield dikes.