My novel The Fifth Day begins with an unnamed beast waking up and finding itself in the world of humans -- and realizing it can recognize artificial from natural structures by their shapes. Here's its first sight of a house with an open garage door:
The thing in front of it was too regular, too square to be a cave, but the opening in the front showed a shadowed interior and the promise of coolness. The cave was a man-structure, probably. Men liked such things, with straight edges and right angles, to show that they could master nature, bend it to their desires, eliminate the rough and the irregular and the uneven.
The suggestion that straight lines don't occur in nature is false, of course. Crystals, for example, have abundant straight lines and perfect angles. The difference (although it probably didn't occur to a mind like the beast's) is a subtle one; humans cut, fold, or shape objects into flat surfaces with straight edges and definite angles for reasons of functionality. We superimpose regularity onto irregular materials from the top down, for our own purposes. In nature, however, the patterns emerge from the bottom up; they're reflections of some underlying regularity of structure. (In crystals, the internal angles of the chemical bonds holding the lattice together.)
So it's not that nature is irregular; it's more that regularity, especially somewhere you wouldn't expect it, demands an explanation.
Which brings us to the two nearly perfectly straight lines that bisect Scotland from southwest to northeast.
The southern one is called the Highland Boundary Fault, and wavers a bit (as you can see from the map); but the northern one, the Great Glen Fault, is just about ruler-straight. As you might guess from the name, the Highland Boundary Fault separates the Highlands (to the north and west) from the Lowlands (to the south and east), and represents a dramatic shift in topography and geology. The Great Glen Fault is even more puzzling, not only because of its oddly perfect geometry, but because it cuts straight across a region of Scotland that is relatively uniform geologically.
Reconstructing what happened here took geologists delving into the deep past. Between the late Ordovician and early Devonian Periods, on the order of from 490 to 390 million years ago, a pair of continents that had joined some thirty million years earlier, nicknamed Baltica and Avalonia, collided with the continent of Laurentia (which makes up the majority of what is now North America, and -- most germane to our discussion -- the northwestern part of Scotland). This gave rise to a series of orogenies (mountain-building episodes), first the Caledonian Orogeny (that raised the Grampian Mountains in Scotland and the Scandinavian Mountains in Norway and Sweden), then the Acadian Orogeny (which raised the Appalachians).
This is a vast oversimplification of what was a complex event, but the gist is that the process that created all three mountain ranges is the same one that is currently creating the Alps and Himalayas -- continental blocks colliding, and raising mountain ranges along the suture. (This is why you can find marine fossils at the tops of the Himalayas; the rock at the peak of Mount Everest was once at the bottom of the a piece of the Indian Ocean that vanished when India slammed into Asia.) After the Caledonian and Acadian Orogenies raised that entire massive mountain range, rifting tore it into three pieces, leaving the longest chunks in eastern North America and Scandinavia, and a smaller piece cutting through Scotland, once again from southwest to northeast.
The fact that the trend of the mountain range is the same as the trend of the two strangely straight faults is no coincidence. The answer seems to be that when Baltica/Avalonia collided with Laurentia, the direction of motion wasn't perpendicular to the coastline. The two approached at an angle, so when the collision occurred, the force wasn't exerted directly into the margin. A component of the force was exerted along the suture, so this created what's called a strike-slip fault -- where the movement is parallel to the fault rather than perpendicular to it. (A famous example is the San Andreas Fault in California.)
And this is what created the two huge faults in Scotland. The southern one, the Highland Boundary Fault, represents the suture line between Baltica/Avalonia (to the southeast) and Laurentia (to the northwest); the Great Glen Fault is just a stress-relieving crack that formed because the sideways pressure from the collision became too high for the rock to bear, and it split along a straight line, creating a deep valley straight across the country that now includes the famous Loch Ness.
So (very) long-ago continental collisions explain the odd geology of Scotland. The drastic difference in the rocks between the Highlands and Lowlands comes from the fact that they started out on different continents -- the Highlands on Laurentia, the Lowlands on Avalonia. The two long faults were created by the stress of the collision, which involved forces large enough to raise mountain ranges that at the time were as high as the Himalayas.
The straight-line cracks in the ground that characterize the topology of Scotland give us a hint about some fascinating underlying causes -- just as the symmetry of a snowflake represents the intricate hexagonal shape of the crystal lattice that forms it, the fact that the Fibonacci series shows up in the arrangement of plant leaves and stems is driven by maximizing the light-catching surface, and the bilateral symmetry of most animals comes from patterns set deep in their evolutionary history. Regularities in nature aren't accidents; noticing things like this, and (more importantly) asking why, is the very basis of science.
As science educator Roger Olstad put it, "Science is, at its core, the search for explanations to account for patterns in our observations."