\ 
OLD RED SANDSTONE OF WESTERN EUROPE, 401 
of fossil fishes are so constantly present as to form a striking feature of the 
strata. ; 
At St-John’s Point layers of red sandstone and shale begin to appear in 
the flagstones, which likewise assume a reddish-grey colour and more sandy 
texture, until at.a fault which runs through the creek called Scotland’s Haven, 
they are succeeded by a higher set of red strata, forming the zone of the Gill’s 
Bay sandstones. | 
Paleontological Distinctions of the Thurso Flagstone Group.—A considerably 
_ larger suite of fossils has been collected from this than from the Wick group, 
"| 
as a 
———  — 
though the general facies remains so similar as to show that the whole vast 
pile of flagstones forms but one natural and continuous series. By far the most 
characteristic paleeontological distinction of the Thurso group is the occurrence 
of fishes belonging to the ganoid sub-order Acanthodide. None of these have 
yet been found in the lower group. Three species of Acanthodes have been 
obtained by Mr Peacu from the flagstones which extend from Mey Hill to 
Strathy. One of these (A. Peachiz), named after its discoverer by Sir PHitip 
EcertTon, has a considerable range, since it occurs not only towards the base 
of the group among the Weydale and Stonegun flags, but at intervals up to the 
top, and even ascends into the highest set of beds in the flagstone series of 
Caithness. But it has not been obtained from lower horizons. Three species 
of Cheiracanthus occur at Holburn Head and among the flagstone quarries to 
the south-east of Thurso. C. grandispinus is rare, and only appears in the 
form of detached spines. C. pulverulentus is more frequent. Three species of 
Diplacanthus have been rarely found at the Hill of Forss, but none of them in 
any other Caithness locality. Of D. crassispinus and D. longispinus only 
‘spines occur. Again, fragments of the large plates of Asterolepis have long 
been known from the labours of Rospert Dick, HucH Mituer, Joun MILLer, 
and C. W. Pracu to be eminently characteristic of the flagstones round Thurso. 
Mr Pracu has only found one piece of this fish from the lower or Wick flag- 
stones at Noss Head. Coccosteus cuspidatus and C. decipiens have a wide range, 
since they occur as low down as the thick beds of Noss Head, and high in the 
thin shaly flags of Mey Hill; but C. puszl/us occurs only in the Thurso group, 
wherein Mr Peacu first observed it in abundance on the shores of Thurso Bay. 
Osteolepis macrolepidotus is another fish with a great vertical range ; it occurs in 
the thick flags to the south of Wick, and on many different platforms up to the 
Huna flagstones. It is specially abundant and beautifully preserved at. Reay. 
0. microlepidotus, on the other hand, does not appear ever to descend into the 
Wick group. But in the Thurso group, and particularly in its lower members, 
this last-named fish is remarkably abundant. As many as a hundred individuals 
_ may be counted within a space of three or four square feet, mingled with re- 
| mains of Acanthodes and Cheiracanthus. It is emphatically the fish of the flag- 
VOL, XXVIII. PART II. 5M 
