Arthur's Seat

The volcano - as opposed to anything you might sit on :O) First geology field trip today - and boy was it cold! Typical Edinburgh-in-spring kind of weather... Very interesting though. I've been up to Arthur's Seat and Salisbury Crags many times (mostly to climb at the Crags), but walking round the whole area and piecing together its geological history puts a different perspective on it.

This is Hutton's section - the second most important geological locality in the world, according to our tutor (the first being Siccar Point in East Lothian - more of that later). The magmatic sill above is sitting on bedded sedimentary strata below, and has intruded into the strata, causing it to turn up at the edge. This feature showed Hutton that there had to be some kind of force behind such intrusions, rather than lava 'seeping' into cracks between sedimentary beds.

The whole area is filled with the evidence of its geological history. From sandstones and mudstones laid down in warm shallow waters, when Scotland was somewhere near the equator - this picture shows distinct rippling caused by gentle wave action - to basaltic sills and lava flows, and the very heart of the volcano itself. The beds and sills have been tilted by folding and faulting and now dip about 30 degrees to the east. The area has also been eroded by the passage of glaciers during the last glacial period, removing the soft sand and mudstones, and exposing the basalt sills - there are even erratics, smooth 'alien' bolders dumped by the glacier on its passage through.

A very interesting day, and a refreshing new look at an area I thought I knew quite well.