In the Mt Lyell area limestone conformably underlying unmineralized Mt Read Volcanics and unconformably overlying mineralized Mt Read Volcanics contains fossils of late Middle Cambrian or early Upper Cambrian age. This suggests an upper limit of late Middle Cambrian or early Upper Cambrian for the mineralization in the Mt Lyell area. The view of Geeet al.(1970) that the Mt Read Volcanics and the fossiliferous Cambrian sequences of western Tasmania are at least partly contemporaneous is confirmed.