back to Scotland

On July 5 we traveled from Edinburgh through the Central Highlands (the Grampian Mountains) to Inverness. Between the Highlands Boundary Fault and the Great Glen Fault we encountered…geological complications! The rocks in this region were squeezed, twisted, baked and changed during the Caledonian Orogeny into a metamorphic terrane of great complexity. In addition, the rocks were intruded by granitic plutons, seen beautifully in the Cairngorms. Historical sights included the Blair Castle and the Culloden Moor where the Scottish Highlanders were defeated by the English armies in 1745. We also made a brief stop at a distillery in Pitlochry.

At the beginning of the day, it looked like we were finally going to have some of that legendary Scottish bad weather, and we literally missed the Firth of Forth in the fog. As we climbed into the Highlands, the clouds cleared, and it turned into a beautiful day...

The gardens at the distillery in Pitlochry were also very beautiful...

See two of my favorite high resolution flower shots here

They say the water is the important factor in the taste of Scotch Whisky, but in the case the water did me the favor of exposing some of the rocks of the Dalradian Schist. And we had precious few chances to pick up rocks this day!

The mountains of the Highlands vaguely reminded me of home near the Sierra foothills. Right down to the occasional clearcutting of the forest.

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What a great "No Littering" sign at Blair Castle!

There weren't many rocks to see at Blair, but had we more time (to hike 14 miles) we could have seen Glen Tilt, where James Hutton found a marvelous exposure of granite intruding into the surrounding sedimentary rocks. At sites like Glen Tilt, he was able to prove the molten origin of granite. On the other hand, the owners of Blair Castle had planted a beautiful forest containing trees from around the world...including California Redwoods (already 180 feet high).

Once again, erosion along the creek provided good exposures of the Dalradian Supergroup rocks.

We started to see more and more evidence of the glaciers that scoured the countryside a few thousand years ago, such as the rounded terrain at Loch Ericht, below:

And then we arrived at Cullodon, where the armies of Bonnie Prince Charlie and the Highland Clans were obliterated by the English army in 1745. It was a sad time for Scotland...

We ended the day with dinner in Inverness, and a delightful walk along the River Ness to see Inverness Castle, built very recently (in 1822!).

The castle was constructed from blocks of Old Red Sandstone. Many of the blocks are actually conglomerate!

Geological Notes:

 The stratigraphy and structure of the Grampian Highlands is very complex, involving the breakup of a continental landmass in late Proterozoic time only to be followed by a continental collision. The ocean that formed between the continents was the Iapetus Sea.

 The Dalradian Supergroup is a sequence of many individual formations and layers deposited in changing circumstances along the developing margin of the landmass of Laurentia in late Proterozoic time. The supergroup is divided into at least four groups:

 The Grampian Group is composed of sandstones and limestones deposited in a passive continental shelf environment. As the continent stretched, normal and detachment faults developed, forming basins in which progressively coarser sediments were deposited as the Appin   and Argyll Groups.

 The Argyll Group is especially intriguing, as it contains evidence of glacial activity. These rocks were relatively close to equatorial regions, and rocks of similar age around the world show evidence of similar activity (veterans of the Death Valley field studies may recall similar rocks found in the Kingston Peak Formation). The world almost froze over in late Proterozoic time! There may have been only a narrow strip of ocean in equatorial regions during this, the most intense ice age ever recorded on Earth. The ice advanced and retreated at least 17 times.

 The Argyll Group also preserves a record of volcanic activity that resulted from the stretching of the earth’s crust as the continental landmass split apart.

 By latest Proterozoic and early Cambrian time, the Iapetus Sea was fairly wide, and Southern Highland Group was deposited as turbidite deposits and greywacke sandstones in deeper water along the continental rise.

The Caledonian Orogeny:

 Later in the Cambrian, and during Ordovician and Silurian time, the Iapetus Sea began to close as subduction zones started to swallow up ocean crust. The Greenland/North American continent (Laurentia) converged on the European continent (Avalonia and Baltica), and the Caledonian Orogeny resulted. The rocks of the Dalradian Supergroup were caught in a vise between the continents and were crushed and heated. Rocks were pushed to great depths within the crust, and a mountain range rose, which extended from the vicinity of Florida all the way to Scandinavia.

 The rocks of the Dalradian Supergroup were changed to varying degrees into metamorphic rock. In some cases the metamorphism was limited, and the original identity of the rocks can be clearly recognized. In other cases the rocks were changed so much that their source couldn’t be determined. The migmatites of the Central Highlands Complex, which we will see as we approach Culloden and Inverness, fall within this category.

Granite intruded into the highly deformed rocks around 400 mya, including a very large batholithic body in the Cairngorms. The subsequent erosion and uplift of the rocks has resulted in spectacular scenery of the mountains. The familiar Old Red Sandstone was deposited along the margins of the Highlands in Devonian time.

As in all other parts of Scotland, Pleistocene glaciers covered most of the landscape, but the highest parts of the Cairngorms protruded above the ice as nunataks.