Rathlin Island lies north of mainland Northern Ireland, a few miles offshore. I spent three lovely days there this past summer, investigating the geology and appreciating the wildlife (puffins and other sea birds, and seals). The geology is pretty straightforward: Paleogene basalt overlying Cretaceous “chalk” (really not so chalky here – technically, it’s the Ulster White Limestone). Here’s a suite of interactive imagery that you can use to explore Rathlin’s geology in a “virtual field trip.”
Google Maps view of the island:
A photo to show the basalt overlying the chalk:
In places the chalk is rich in chert nodules:
The chalk contains beautiful belemnite fossils:
Here’s another fossil of some sort. Anyone able to identify it?
Lithophagus clams bore holes into the chalk, and dwell therein:
These are modern critters, occupying a Cretaceous substrate. They are not fossils.
On the west side of the island, sea stacks provide nesting places for a LOT of seabirds:
Okay, now that you’ve run your eyeballs over those photos, consider some GigaPans:
Gazing over the pastoral scene on the Roonivoolin Trail, you don’t really get a sense of the geology:
[gigapan id=”188460″] Link GigaPan by Callan Bentley
…But basically the island is made of Paleogene basalts slathered over Cretaceous “Chalk” (the Ulster White Limestone, technically), as the next two GigaPans show:
[gigapan id=”188430″] Link GigaPan by Callan Bentley
[gigapan id=”188426″] Link GigaPan by Callan Bentley
The basalt dominates the outcrops you’ll see walking around the island. See if you can find some laterite in this view:
[gigapan id=”188432″] Link GigaPan by Callan Bentley
The West Light bird sanctuary features some horrifically stinky seabird nesting colonies (puffins!!) atop sea stacks eroded into the basalt:
[gigapan id=”188447″] Link GigaPan by Callan Bentley
[gigapan id=”188448″] Link GigaPan by Callan Bentley
A weathered outcrop of basalt nearby the bird sanctuary visitor center:
[gigapan id=”188463″] Link GigaPan by Callan Bentley
Let’s head down to the shore next, and take a look at the beach. You might find some seals in this image:
[gigapan id=”188566″] Link GigaPan by Callan Bentley
The beach there hosts a nice variety of sediment. The contrast between the chalk and basalt cobbles is striking:
[gigapan id=”188567″] Link GigaPan by Callan Bentley
[gigapan id=”188429″] Link GigaPan by Callan Bentley
Here’s a Petri dish full of a slightly finer collection of sediment from the shores of Church Bay:
[gigapan id=”190501″] Link GIGAmacro by Robin Rohrback
And a finer, wind-sorted fraction of the sediment that accumulated higher up the berm:
[gigapan id=”190457″] Link GIGAmacro by Robin Rohrback
Here’s a cobble of the basalt, showing well-developed amygdules in its vesicles:
[gigapan id=”191392″] Link GIGAmacro by Robin Rohrback
Front and back of a cobble of the Ulster White Limestone, showing a cross-section through a belemnite:
[gigapan id=”191417″] Link GigaPan by Callan Bentley
The obverse really shows the radial arrangement of the calcite crystals in the belemnite’s rostrum:
[gigapan id=”191582″] Link GigaPan by Callan Bentley
Scanning electron micrograph (SEM) GigaPan of the Ulster White Limestone. You’ll find some coccoliths in there – the little plates surrounding the coccolithophore organism which is the source of chalk:
[gigapan id=”191435″] Link SEM GigaPan by Robin Rohrback
And finally, an SEM image of a foram from the fine sediment sample. Somewhere, you’ll find a diatom hiding in its interstices!
[gigapan id=”191436″] Link SEM GigaPan by Robin Rohrback