Complex sentence: Pre-Cambrian in origin and about 1.7 billion years old; there are various igneous intrusions including pegmatite, as well as "bands" of gneiss and schist.
Split into simpler sentences: Pre-Cambrian in origin and about 1.7 billion years old,. There are various igneous intrusions including pegmatite, as well as "bands" of gneiss and schist.