Right at the sho­re­li­ne of Lake Vänern, by Råbäck har­bour, we can see how the first sedi­ments of the tab­le mountains were depo­si­ted on the Precam­bri­an Basement.

One good pla­ce to see this is a short distan­ce north of the har­bour, on the lake side of the cobb­le field. The­re is a small head­land here that you can walk out to.

The bed­rock bene­ath the tab­le mountains has been ero­ded to a rela­ti­vely flat sur­fa­ce. Around 550 mil­li­on years ago Swe­den was situ­a­ted south of the equa­tor. In a shal­low sea, sedi­ment was depo­si­ted on top of the older bed­rock. This soli­di­fi­ed and beca­me the sedi­men­ta­ry rocks that we see today at the base of the tab­le mountains. This con­si­sts of a met­re-thick lay­er of conglo­me­ra­te. A conglo­me­ra­te is a type of rock made up of roun­ded sto­nes (roun­ded by the action of water, for examp­le by waves on the sho­re or in a river­bed) that are bound toget­her. On the rocky sho­re­li­ne near Råbäck har­bour you can see how the conglo­me­ra­te has been depo­si­ted in poc­kets and cracks in the Precam­bri­an Base­ment. Sand­sto­ne was then depo­si­ted on top of the lay­er of conglo­me­ra­te, and this can be seen as a clear ter­ra­ce in the wood­land a short distan­ce from the sho­re. The sand­sto­ne lay­er con­tains fin­dings after fos­sils and waves (ripp­le marks). The­se tell us about the envi­ron­ment that existed here more than 500 mil­li­on years ago – an impor­tant pie­ce in the puzz­le of understan­ding Earth’s development.

Hit­ta Hit