Fossils of trilobites and hyolithids were first identified in the Llanberis Slate of Penrhyn Quarry, Bethesda, North Wales, in 1888, and were reviewed in 1950, leading to the assignment of an early Cambrian (Stage 3, series 2) age. Recent collections from the Upper Green Slate Member of the Llanberis Slate include organisms associated with Burgess-Shale-type Konservat Lagerstätten. Despite low - grade metamorphism of the deposit, a substantial diversity of taxa is recognisable, including sponges, non - trilobite arthropods, vetulicolians, putative sipuncula and other worms. The value of Lagerstätten is the insight they provide into the composition of infaunal and epifaunal communities, including weakly - sclerotised organisms whose identity may only be inferred where the taphonomy is restricted to biomineralised elements or ichnofossils. Exceptional preservation from Cambrian localities including the Burgess Shale of British Columbia and the Maotianshan Shale of Southern China, have provided a benchmark against which formerly unidentified material can be assessed. This fauna is now known to occur World - wide, but good examples from the Avalonian terrane, comprising Southern Britain and Eastern Canada in Cambrian times, have not previously been identified.

This is the first record of a Burgess Shale - type fauna in the Cambrian strata of Wales, where it represents the oldest comprehensive early Cambrian biota from the historical type area on which the Cambrian System was originally based. Many of the organisms described also represent the first records from North Wales, and, in an international context, it is also the first record of a Cambrian Burgess Shale - type assemblage from Avalonia.