Sten – Uppsala

I am a loose round block of rather coarse-grained gneiss granite, excavated from Uppsalaåsen. Uppsalaåsen is a very long sand and gravel ridge that runs through all of Uppland from Älvkarleby in the north to Ekerö in the south and probably continues even further, and no one has told me where they dug me up, inside Uppsala or in some gravel pit somewhere else, so I do not really know. What I do know is that Uppsalaåsen is a glacial esker that was formed by an ice river with meltwater from the inland ice when it melted about 10,000 years ago. The ice river flowed in a tunnel under the ice cap and brought with it a lot of gravel and sand and larger stones that the ice had scraped off the bedrock surface and which then lay frozen inside the ice. In the gushing melt waters from the glacier, the stones and gravel and sand tumbled around so that we became quite dizzy, and tore against each other so that we became rounder and rounder in shape, especially the larger stones and blocks. This is why such eskers are called ”rullstensåsar” in Swedish, because they are filled with round stones that have rolled around in the water. When we got to the edge of the ice sheet, where the ice river flowed into the sea (at that time the whole of Uppland and the Mälardalen area was under water), we sank to the bottom and formed a ridge of sand, gravel and stone, a glacial esker. As the ice melted and the ice edge moved further north, year by year and decade by decade, the esker grew in length further and further north.

So I don't really know where I'm from, or even if I'm from Uppland and Uppsala county to start with, before I was broken off from the solid bedrock by the inland ice, carried south frozen in the ice while it slowly slid south, and then loosened when the ice began melting, fell into the ice river, and was washed with the water masses even further south until I finally became part of the Uppsalaåsen esker. I can come from quite far north, perhaps from the bottom of the Bothnian Sea, or from southern Norrland. Or I may be after all of more local origin, perhaps somewhere from northern Uppland.

But you can see from my appearance that I, like several other stones in the stone circle, am a piece of gneiss granite, i.e. a granite that was formed from a magma that solidified deep in the earth's crust and then was exposed to pressure, continued heat and movements that caused the mineral to form parallel elongated streaks, a gneissic structure that makes me into a gneiss granite. Maybe not so obvious, mostly I look like a grey-speckled or slightly red granite, but you can probably guess a slightly gneissic structure in me, or what do you say? Such more or less gneissic granites are a very common rock type in Sweden, probably the most common. Uppland's bedrock consists largely of such gneiss granite, sometimes called Uppsala granite, which is between 1870 and 1910 million years old. Even if I were to come from further north, say from Gästrikland or Hälsingland, I would be about the same age, or maybe a little younger, around 1860 million years. Somewhere between 1860 and 1910 million years is my age anyway, so we can say somewhere in the middle, about 1880 million years.

Geologist Åke Johansson
Swedish Museum of Natural History