344 
VOLCANOES OF THE LOWER OI^D RED SANDSTONE book v 
E. N. Peach and J. Horne have added a fourth centre in the Orkney Islands. 
At present, therefore, we are acquainted with the records of four separate 
groups of volcanic vents in Lake Orcadie. 
Tlie southern margin of this water-basin appears to have indented the 
laud with long fjord-like inlets. One of these now forms the vale of Strath- 
bogie, which runs into the hills for a distance of fully 20 miles beyond 
what seems to have been the general trend of the coast-line. In this valley I 
found a bed of dark vesicular diabase intercalated among the red sandstones 
and high above the base of the formation, as exposed on the west side of the 
valley near Bum of Craig. On the east side a similar band has since been 
mapped for the Geological Survey by Mr. L. Hinxman who has traced it 
for some miles down the Strath.^ Tliis latter band, as shown in Fig. 101, 
lies not far above the bottom of the Old Bed Sandstone of this district, and is 
thus probably distinct from the Craig outcrop. There would thus appear to 
be evidence of two separate outflows of ba.sic lava in this fjord of the Old 
Eed Sandstone period. 
H 0 vestige has here been found of any vent, nor is the lava accompanied 
with tuff. The eruptions took place some time after the earlier sediments 
Fm. 101. — Section across Stratlibogie, below Rhyme, showing the rosition of the volcanic hand. 
1. Knotted schists ; 2. Diorite intrusive in soliists ; 3. Old Red Conglomerate ; 4. Volcanic hand ; 5. Shales with 
calcareous nodules ; a. Sandstones of Bhynie ; 7. Shales and sandstones, f, Fault. 
of the basin were accumulated, but ceased before the thick mass of upper 
sandstones and shales was deposited. A section across the valley gives the 
structure represented in the accompanying diagram (Fig. 101). 
Twenty-five miles further north a still smaller andesite band has been 
detected by Mr. J. Grant Wilson among the sandstones and conglomerates 
near Buckie.^ It is a truly contemporaneous flow, for pebbles of it occur in 
the overlying strata. But again it forms only a solitary bed, and no trace 
of any accompanying tuff has been met witli, nor of the vent from which it 
came. Both this vent and that of Stratlibogie must have been situated near 
tlie southern coast-line of the lake. 
At a distance of some 90 miles northward from these Moray Firth 
vents another volcanic district lies in the very heart of the Orkney Islands.® 
The lavas which were there ejected occur at the south-eastern corner 
of the island of Shapinshay, where they are regularly bedded with 
the flagstones. They consist of dark green olivine-diabases with highly 
^ See Sheet 1 6 of the Geological Survey of Scotland. 
See Sheet 95 of the Geological Siu'vey of Scotland and Trans. Roy. Soc. Rdin. vol. xxviii. 
(1878), p. 435. 
* Messrs. B. N. Peach and .T. Horne, Pi-oc. Roy. Phys. Soc. Rdin. vol. v. (1879), p. 80. 
