Bamble is dominated by two types of landscape with completely different geological histories. In the west the landscape is dominated by ancient basement bedrock, whereas limestone's are characteristic further east from the peninsula of Langesundsøya.
The division between these two rock types is clearly visible in the terrain and is easy to see from Rognstranda. The lovely ice-polished bedrock on Rognstranda is mainly ancient gneisses. ( ca. 1.3 3 billon years old), and they lay deep within a mountain chain.
From the smooth beach bedrock a sharp edge juts up in the east, with "horizontal stripes". These are limestone's that are "only" about 450 million years old. At that time, the continental plate that Norway was a part of lay south of the equator, and the entire country was covered by a shallow tropical sea teeming with life. Remains of the shells from this life make up the limestone's that one sees for example in the small cliff of the other side of Rognstranda. This edge also dominates the landscape along the E 18 highway through Bamble, for example Høgenhei.