The western seaboard of the Western Isles is world renowned for a habitat called the 'machair'. I'm no biologist and know only the very basics about it.
The bedrock of the islands is Lewisian gneiss, the oldest rock to be found on the surface of the earth. It is 3,000 million years old, and can be found open and exposed at the Butt of Lewis. It breaks down into very poor soil, where precious little will grow. Added to that the preponderance of peat, which creates an acidic environment, and you have a situation where not a lot will grow.
Until recently, the islanders would take their cattle to a shieling inland during the summer for them to gain strength. It was not unheard of for cattle to die of starvation during the winter, whilst grazing the very poor grass by the seashore.
What happens on the seashore is that sand gets blown in, to cover the soil. Sand from the sea contains calcium, more precisely calcium carbonate. This compound is found in seashells. It is also an alkaline, which will neutralise the acid from the peat. And now a very fertile environment is created. During a few short weeks in summer, the machair will come alive in a dazzling display of flowers. Orchids galore, it's a sea of yellows, whites and all colours. I've included a few images I shot during the past summer, to give an indication.
Flowers on the machair at Swainebost (Ness)
Flowers on the machair at Eoropaidh (Ness)
Machair at Barvas (Loch Street)
Machair flowers at Bostadh (Great Bernera)