The early eruptive stages of Mount St. Helens are known as the Ape Canyon Stage (around 40,000-35,000 years ago), the Cougar Stage (ca. 20,000-18,000 years ago), and the Swift Creek Stage (roughly 13,000-8,000 years ago). The modern period, since about 2500 BCE, is called the Spirit Lake Stage. Collectively, the pre-Spirit Lake stages are known as the ancestral stages. The ancestral and modern stages differ primarily in the composition of the erupted lavas; ancestral lavas consisted of a characteristic mixture of dacite and andesite, while modern lava is very diverse (ranging from olivine basalt to andesite and dacite).(p214)