Complex sentence: It is at the southernmost limit of glaciation and the smooth rounded form is evidence of the valley previously being a glacial melt-water channel; which has resulted in alluvial soils being deposited in the valley with chalk, clay and flint on the valley sides.
Split into simpler sentences: It is at the southernmost limit of glaciation and the smooth rounded form of the valley is evidence of the valley previously being a glacial melt-water channel. This has resulted in alluvial soils being deposited in the valley with chalk, clay and flint on the valley sides.