Unless contained within artificially maintained banks, rivers are rarely straight. Meanders are formed as a river flows sinuously across any flat area. Although the cause of meandering is not fully understood, it is known that rivers assume this shape because less energy is then used in the discharge of the water than would be necessary if their courses were shorter and straighter.
The meander pattern that can be seen on the valley floor at the Seven Sisters Country Park is a landscape remnant from a time when the river Cuckmere followed a different course. In 1847 a straight cut was put in the river which effectively diverted any flow from the meanders and instead sent it straight up the river to beyond the causeway (which the A259 now passes over).
Until 500 years ago the whole of the valley was a salt marsh as a result of rise in sea level in historic times. The silt in the meanders forms as a result of this, and some of these silt deposits date back to between 4000 and 1200 B.C. Below this silt sits a layer of sand and gravel which came to rest there as a result of sea levels rising at the end of the last Ice Age.