Abounding in (sea)shells; of a geological formation, consisting wholly or mainly of shells.

Of geological formations or deposits: Consisting wholly or largely of (sea)shells (esp. in a triturated or powdery state, shell-gravel, shell-grit…

Of the nature of shells, shelly.

Abounding in (fossil) shells, conchiferous.

Geology. Characterized by the presence of shells.

Of limestone: containing shells of foraminiferans, esp. orbitoids. Also: relating to, characteristic of, or designating such foraminiferans.