404. : ' PROFESSOR GEIKIE ON THE 
but it may be the same as some of the red freestone associated with the flag- 
stone series in Orkney. 
8. Huna Flagstones.—To the alternations of red sandstone and flag- 
stone on the east side of the Ness of Quoys a group of flagstones succeeds, 
having characters similar to those already described in the Thurso Bay 
and Pentland Firth sections. The flagstones are thin-bedded, blue, grey,’ 
and yellowish, flaggy and shaly strata, often strongly calcareous. They dip 
a little to the north of east at from 8° to 15°, and their thickness may be 
estimated at 1000 feet. Some of the strata contain well preserved re- 
mains of fishes. Among the fossils we still meet with Dipterus macrolepi- 
dotus and Osteolepis macrolepidotus. The little Coccosteus (C. pussillus) and 
the Acanthodians, so characteristic of the Thurso flagstone group, occur 
likewise here. From the strike of the beds, and from similarity of dip and 
lithological features, this group appears to pass across the Pentland Firth to 
form Stroma, the most southerly of the Orkney islands, whence it no doubt 
extends northwards into other members of that archipelago. 
9. John 0 Groat’s Red Sandstones and Flagstones—The Huna flagstones 
occupy the shore as far as the east side of the Ness of Huna, where they 
are succeeded by another mass of false-bedded red sandstones, with in- 
tercalations of blue flagstones. The line of junction between the two groups” 
is here, again, along a line of fault. But as the strata are so little disturbed 
by the dislocation, and the prevailing gentle dip towards E. 10° N. continues” 
on both sides of it, the amount of displacement is probably trifling. The 
red sandstones which now appear much resemble those of Gill’s Bay. They 
occur in successive thicker zones, between which lie many alternations of red 
sandstone, red and blue flagstones, grey shale, and impure limestone. These 
latter strata are quite undistinguishable from portions of the older flagstone 
groups. The highest part of the group consists of a thick mass of false-bedded 
red sandstone, without flagstone or shale. Fossils occur in some of the blue 
flagstones and impure limestones on the beach to the east of John o’ Groat’s 
House. Among these may be noticed Acanthodes Peachii (Eg.), Dipterus sp. 
nov., Pterichthys Dicki (Peach)—the only known Pterichthys from the Old Red | 
Sandstone of Caithness; T'ristichopterus alatus (Eg.), another peculiar form; | 
and Holoptychius Sedgwicku (M‘Coy).* These highest members of-the series are” 
thus distinguishable by their ichthyic remains. Their plants, also, are perhaps 
more varied in kind than those of any other member of the Caithness flag- 
stones. Mr Peacu has obtained from them the same Lepidodendron (allied to” 
* T cannot distinguish between this species and a Glyptolepis. On mentioning this to my friend Dr 
Traquair, he fully corroborated my suspicions, and said that he believed it to be only G@. leptopterus. — 

