III.— Note on the chemical composition of conglomerates of Lower and Upper Old Red Sandstone age from Ardmore Peninsula, Dunbartonshire

Abstract

Brick-red sandstones and conglomerates of Upper Old Red Sandstone age unconformably overlie chocolate-brown to purple-brown sandstones and conglomerates of Lower Old Red Sandstone age on Ardmore Peninsula, Dunbartonshire. The unconformity is well shown on the western side of the peninsula in the tidal area of the River Clyde (Nat. Grid: NS 788313) and a conglomerate from each formation has been analysed (Table 1). The specimens crushed for analysis were collected as close as possible to the plane of unconformity by Mr. Edward Scorgie during a study of the peninsula ( Trans. geol. Soc. Glasg., 22, 295). Fragments greater than one inch across were separated and not included in the crushed samples. The Lower Old Red Sandstone conglomerate is made up essentially of fragments of quartzite set in a siliceous matrix with a red iron oxide cement. The fragments in the Upper Old Red Sandstone conglomerate are predominantly low-grade Dalradian schists containing variable amounts of quartz, chlorite and muscovite. The matrix is dominantly siliceous and is cemented by calcite and red iron oxide. These petrographic characters are reflected in the chemical analyses: the relatively greater amount of SiO2 in the Lower Old Red Sandstone conglomerate (Table 1—A) is the result of the abundance of quartzite fragments while the relatively greater proportions of TiO2, Al2O3, FeO, MgO and K2O in the Upper Old Red Sandstone conglomerate (Table 1—B) result from the presence of schist fragments. The CaO and CO2 proportions reflect the carbonate fraction of the matrix, which is more abundant in the This 250-word extract was created in the absence of an abstract