CH. XXII LATEST ERUPTIONS IN THE NORTH OF SCOTLAND 
353 
That these volcanic orifices were active about the same time with those in 
the opposite island of Hoy may be legitimately inferred. 
These northern volcanoes made their appearance in a district where 
during the preceding Lower Old Eed Sandstone period there had been 
several widely separated groups of active volcanic vents. So far as the 
fragmentary nature of the geological evidence permits an opinion to be 
Fig. 106. — Groiiiul-plan of voleaniu neck pieroing tlie Caitliues.s Flagstone series on tlie beach near 
John o’ Groat’s House. 
formed, they seem to have broken out at the beginning, or at least at an 
early stage, of the deposition of the Upper Old Eed Sandstone, and to have 
become entirely extinct after the lavas of Hoy were poured forth. Eo 
higher platform of volcanic materials has been met with in that region. 
With these brief and limited Orcadian explosions the long record of Old 
Eed Sandstone volcanic activity in the area of the British Isles comes to 
an end.^ 
^ Tliere appear to be traces of volcanic eruptions contemporaneous with the Upper Old Red 
Sandstone of Berwickshire, but as they merely formed a prelude to the great volcanic activity of 
Carboniferou.s time, they are included in the account of the Carboniferous plateau of Berwick- 
shire in Cliapters xxiv. and xxv. 
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