Mitchell
et al. (1970) and Garson et al. (1975), who adopted the name
Phuket Group for the entire succession beneath the Ratburi
Limestone in upper Peninsular Thailand, found that they could
divide the succession into only two mappable units which they
named informally the ‘Upper Formation’ up to 200 m thick
comprising mudstones, thick-bedded sandstones and shales with
a bryozoa-rich shelly fauna in its lower part, and the ‘Lower
Formation’ of unknown thickness which is essentially barren of
fossils. (The name Phuket Group has been dropped among
geologists in Thailand, but is retained here as it highlights the
different successions in the upper and lower Peninsula).