抄録
There are developed strata of conglomerate, sandstone, and mudstone of Oligo-Miocene to Lower Miocene ages in the Chichibu basin., The Akahira formation, one of the Tertiary formations, unconformably overlies the pre-Tertiary sedimentary rocks in the northern and western margins of the basin., The purpose of this paper is to differentiate the heavy minerals included in the lowest part of the formation, and to investigate the source rocks of the sediments., The results obtained are as follows: 1., In the northern part of the basin, fairly large euhedral or angular crystals of allanite, anatase, biotite, epidote, garnet, titanite, tourmaline, zircon, augite, and hypersthene are commonly found., Green and brown hornblende, topaz, barite, and olivine are found in only a few samples., On the other hand, only few rounded garnet, titanite, zircon, and some other minerals are found in the western part., 2., It is possibly said that the sediments in the northern marginal part were derived not only from pre-Tertiary sedimentary rocks but also from granitic and basic igneous rocks., 3., The texture of the heavy minerals indicates that the source area of the granitic rocks might not be far from the basin., 4., There is no evidence that the sediments were derived from the Nagatoro system which consists of crystalline schist.,
