J. Stone collecting glacial erratics off Wells Ridge for cosmogenic isotope exposure dating. Rock in foreground is Paleozoic (Cambrian) Swanson Formation, greenschist facies metagraywacke and metaturbidites of oceanic origin.Rock on peaks behind is Byrd Coast Granite, a Cretaceous leucogranite (granite) with A type chemistry. West Antarctica.: Louis Sass: Arctic & Antarctic photographs, pictures & images from Bryan & Cherry Alexander Photography.