The rocks composing Piz Bernina are mostly diorites and gabbros. The youngest of the Precambrian rocks are the South Charnwood Diorites. The igneous rocks found include&colon; quartz monzonites, granites, diorites, gabbro, diabase, and andesite. Along the western edge of Charnwood Forest the rocks are mainly Precambrian igneous diorites. Granites, syenites, and diorites, covered with Laurentian metamorphic slates, occurred extensively in the north-west.