further down. The fall is 149 meters. The entire river course is in the construction zone, while the precipitation field is in Nordmarka. The rocks in the ground below the river are syenite (northern market) and hornfels from Bjølsen and northwards, while the ground south of Bjølsen is mainly clay slate and tuber lime. Syenite and hornfels are hard rocks that are hard to decompose. The river is located in the geological Oslo field, where subsidence areas are formed by stretches in the earth's crust, blocks are separated and middle parts sink in, allowing for rivers to cut down. The softer rocks further south hard formed the basis for brickwork on Myraløkka and Øvre Foss (Våghalsen), which in the 1840s was the country's largest, and large slides in the river, hence the street name Leirfallsgata at the bottom of Grünerløkka. In Øvre Foss lies a slab of solidified volcanic melt that has come up in a crack, which is tougher and harder than lime and slate and a reason why the waterfall is here. Up in Nydalen, there are steep erosion cliffs that are part of the Grefsen moraine. The river has cut its way through thick masses of gravel, sand and clay that formed in front of the inland ice that receded about 9800 years ago (the Akert Step). At the largest bathtub at Stilla and at the gutters between the grasslands at Brekkedammen, there is visible syenite (circular swab) with clear scouring strips from the glacier. At Nedre Foss there is visible tuber lime, black clay slate and limestone (orthocer lime). About 10,000 years ago, the sea rose 220 meters higher than today, about 9300 years ago the sea was 150 meters so that the Maridal waters were separated from the fjord and the Akerselva was born. , 6,000 years ago was the waterline at Myraløkka and 3,000 years ago at Cuba. Waterfalls The 20 waterfalls are, from above: Kjelsås fall Brekkefossen Nydalsfossen, also called Nygårdsfossen Gullhaugfossen, at Gullhaug square Bjølsenfossen (two falls, fall height 16 meters), at Treschow's bridge Lilleborgfossen, fall height 3 meters Hjulafossen, below the Vøyen Bridge, which together with the Våghalsen form the Vøyen Falls Daredevil, below the Beyer Bridge Upper Waterfall, also called the Seilduksfossen Nedre Foss, several falls, at the silo in Cuba A lot of stone has been used in river banks and bridges: At the Vaterland Park, a rocky mountain