Original: Bays form where weak (less resistant) rocks (such as sands and clays) are eroded, leaving bands of stronger (more resistant) rocks (such as chalk, limestone, granite) forming a headland, or peninsula.
Simplified: Bays form where weak rocks, such as sands and clays, are eroded, leaving bands of stronger rocks, such as chalk, limestone, or granite, forming a headland, or peninsula.