Abstract: The sedimentary, volcanic rocks occuring north-northwest of highly deformed, metamorphosed rocks of Seyitgazi-Eskişehir anticlinorium are discussed in this paper. The Tertiary sedimentary rocks of terrestrial, lacustrinefades were deposited in the Southern Eskişehir cuvette. Terrestrial fades consist of grits, sandstones, clays, marls with plant remains a basal conglomerate with serpentinite boulders. Lacustrine fades on the other hand, are mainly made of argillaceous, tuffaceous limestones, limestones, marls, conglomerates, tuffs. These oldest sediments, pyroclastics of the cuvette were formed during the Lower Miocene. Pliocene volcanic rocks consist of flat-lying basic-intermediate lava flows, occur at the Lower-Upper Neogene sedimentation break. Upper Neogen sediments/ found as thin bands over the intermediate basaltic volcanic rocks, consist of marls, limestones. The acid volcanic actvity of Lower Miocene age which produced the unwelded tuffs (sillar) occured prior to the deposition of the oligomict conglomerate formation, probably continued to a lessr extent gwing rise to the tuffaceous limestones. The basic intermediate (benmoreite) lava flows of Pliocene age followed, the formation, erosion of these sedimentary, pyroclastic rocks of the lacustrine fades.

The sillar, benmoreite, tuffaceous limestone, the matrices, cements of dolomitte, calcarous conglomerates are studied, in detail, petrochemically ,some suggestions are made to explain their petrogenesis.