The dating was based on graptolite fossils which were identified as " Monograptus uncinatus ", which is of early Ludlow age ( around ).
2.
The group is poor in fossils, with the exception of graptolites; of these " Cyrtograptus grayae " and " Monograptus exiguus " are zonal forms.
3.
The boundary is defined as the first appearance of the graptolite " Monograptus austerus sequens " ( the base of the " Monograptus triangulatus " biozone ).
4.
The boundary is defined as the first appearance of the graptolite " Monograptus austerus sequens " ( the base of the " Monograptus triangulatus " biozone ).
5.
In Denbighshire and Merionethshire the upper portion of the Denbighshire Grits belongs to this horizon : viz . those from below upwards, the Nantglyn Flags, the Upper Grit beds, the Monograptus leintwardinensis beds and the Dinas Bran beds.
6.
The age of " Baragwanathia " has been uncertain because the fossils described by Lang and Cookson ( 1935 ) at first appeared to be of Late Silurian age, associated as they were with the graptolite genus " Monograptus ".
7.
However, the Silurian ( Ludlovian ) dating of the deposit in Victoria, Australia which produced the type specimens of " Baragwanathia longifolia " was later disproved, as " Monograptus " ( and in particular the species present at that site ) was later proved to persist into the Early Devonian.
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