The
pretertiary rocks represent the oldest sediments exposed here. They
consist of phyllite, schist, gneiss, serpentine and crystalline
limestone, and up the Goenoeng (hill mountain) Konang, G. Djokotoewo
and G.Toempeng, G.Merak, G. Djabalkat, G.Wonosari, G. Pegat, G.
Tapan. The Kali (river) Dengkeng has cut the pretertiary area in two
parts, and we can only explain this curios fact by the hypothesis
that its present course is a supermposed one. Verbeek and Fennema
belived the phyllite and schist series to be of cretaceous age
because of its similarity with phyllites and schist of the Loh Oeloh
area (Some 150 km west) which were khown to enclose limestone beds
with Orbitolina sp. In the Pretertiary of Djiwo, no fossiliferous
beds have been found, excepting a few limestone localities containing
radiolarian, unsuitable for determination of geological age. Recently
boulder of Orbitolina limestone have been found near desa Santren,
probably derived from a Neogene conglomerate, which shows that at
least part of the pretertiary substratum is of creatceos age. The
pretertiary sediments from an anticline with south westerly dipping
of the axis.
