OLD RED SANDSTONE OF WESTERN EUROPE. 405 
L. Gaspianum) which occurs so frequently in the northern flagstones from 
Huna to Reay. Another is, according to Dawson, “obviously of the same 
type as his Cyclostigma densifolium;” a third is “a Cyclopteris of the type of 
C. Brownii,” while a fourth is “a Calamite resembling C. transitionis.”* Other 
less determinable forms, including also a Stigmaria, occur. The general 
resemblance of this vegetation to that of pre-carboniferous lands in Canada is 
interesting in its bearings upon palzeozoic geography. 
The total thickness of the John o’ Groat’s group maybe set down at about 
2000 feet. Its component strata are seen in a continuous ascending section as 
far as the Ness of Duncansbay, where the thick zone of red sandstone forming 
the highest visible portion of the group bends into a trough, and rises again with 
a north-westerly dip, which increases in steepness until a fault on the south 
side of Duncansbay Head brings up a mass of grey flagstones to form that 
grim, steep-walled and deeply-cleft headland. To the south of Duncansbay 
Head a range of red sandstone cliffs, separated from the flagstones of the pro- 
montory by a well-exposed fault, range southwards for more than a mile and 
a half, until by another dislocation the grey flagstones are again brought up at 
Fast Goe. ‘These Duncansbay red sandstones have much in common with 
those of Dunnet Head and Hoy, with which, in the absence of fossil evidence, 
IT would provisionally place them. They will therefore be again referred to 
in connection with the development of the Upper Old Red Sandstone. 
In the centre of the synclinal trough at the Ness of Duncansbay lie the 
only igneous rocks which (with the exception of occasional basalt dykes, pre- 
sumably of Tertiary date) I have met with in the Old Red Sandstone of Caith- 
ness. Their interest is heightened by the fact that they include both crystal- 

OF BEACH 
Fig. 7.—Plan of Volcanic Neck in Red Sandstones on Beach near John 0’ Groat’s. The arrows show the dip of the sand- 
_ stones. The dark vein and two patches in the neck are of diabase. 
line and fragmental materials, and that they point distinctly to volcanic activity | 
jin this part of Scotland at some time subsequent to the consolidation of the 
= o Groat’s sandstones. The above rough eye-sketch shows the general 
her * Dawson on Fossil Plants of Devonian Rocks of Canada, “Memoirs of Geol. Surv.” Canada, 
4 
| VOL. XXVIII. PART II. 5.N 
