lxx FLORA ORCADENSIS. 
which were originally the beach gravels that encircled 
a granite islet, but these conglomerates are at a 
high level in the sequence, and do not correspond in 
position with those that occur in great thickness 
around Berriedale and in Morven and Maiden Pap 
in the south of Caithness. 
The West Mainland of Orkney contains the oldest 
rocks that occur within the boundaries of the county, 
if we leave out of consideration the Stromness granite 
and eneiss, which are of vastly greater antiquity than 
any of the Old Red Sandstone deposits. The dark 
grey flagstones of Stromness, Sandwick, and the west 
of Birsay contain a group of fossil fishes which belong 
to a lower horizon in the stratigraphical sequence than 
those found in the rocks of the East Mainland and 
the North Isles. The Stromness beds with the fishes 
entombed in them correspond in age to the Achanarras 
beds of Caithness, and to the sandstones of Cromarty, 
Inverness, and Banffshire. The East Mainland and 
North Isles are in part underlain by flagstones of 
the same age and containing the same fishes as the 
flagstones of Thurso. Still higher in the Orcadian 
Old Red Sandstone are the yellow and red sand- 
stones and the dark-red clays or marls that occur 
near Roeberry, in South Ronaldshay ; and in 
Deerness, Shapinshay, and Eday. These are dis- 
tinguished not only by their lithological characters, 
but also by the occurrence in them of a distinct 
assemblage of fossil fishes. The rocks of this group 
were first proved to be fossiliferous by Charles Peach, 
who investigated them at John O’Groat’s, in Caith- 
ness, and since then have been known as the John 
