18th February 2006
ARTHUR'S SEAT
Tour:  Geo                   Participants:  8
Weather:   pleasant weak winter sun, hazy views, becoming cloudier.

   

We started the excursion near the Commonwealth Pool, and began by studying the fine vertical columns in the Samson’s Ribs intrusion  
(locality 29 *): 
Samson's Ribs

We looked at 2 exposures of basalt alongside the Queen’s Road (locality 15), the first showing smoothing by passage of ice and the second scratching and polishing along a fault plane (slickensides). 

The main vents for the eruptions of Carboniferous times on Arthur's Seat were at the Lion's Head and the Lion's Haunch:
Lion's Head and Haunch
....here, we noticed the two principal rock types to be found in the heart of the volcano – dark, fine-grained basalt and crumbly agglomerate, the latter often containing volcanic bombs and mixed sedimentary material caught up in the vent: 
Basalt at left, agglomerate at right.
                                             Agglomerate
To the north-west was the sill intrusion of Salisbury Crags:
Salisbury Crags
... and to the north-east, a succession of lava flows, all dipping at about 25 degrees to the east. Some of the lava flows are likely to have derived from the Edinburgh Castle vent rather than from Arthur’s Seat.

....and here are some images from earlier visits:
                    Salisbury Crags and the location of Hutton's Section.
Hutton's Section
[ * Localities refer to those in the leaflet "Discovering Edinburgh's Volcano", published by Edinburgh Geological Society].
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