Mount Pleasant Caldera rock. The Intercaldera Sequence comprises formations that crop out from overlying flows in triangularly shaped area, and includes thick volcanic ash (tuff), thick breccia layers, and intermediate to felsic igneous rocks that tend to intrude the above layers and are typically located along caldera margin faults. The Exocaldera Sequence contains ash flow tuffs, mafic lavas, alluvial redbeds, and porphyritic felsic lavas that are distributed across five different layers. The late Caldera-Fill Sequence contains rocks that are similar to those of the outflows of the other, older layers, and comprises two formations and two relatively minor intrusive lava flows. The volcanic
Felsic need to be named after their phenocryst mineral, such as 'hornblende-bearing felsite'. The chemical name of a felsic rock is given according to the TAS classification of Le Maitre (1975). However, this only applies to volcanic rocks. If the rock is analyzed and found to be felsic but is metamorphic and has no definite volcanic protolith, it may be sufficient to simply call it a 'felsic schist'. There are examples known of highly sheared granites which can be mistaken for rhyolites. For phaneritic felsic rocks, the QAPF diagram should be used, and a name given according to the granite nomenclature.