While most of the rock in the Peace Park is metasedimentary in nature, late in the Proterozoic some igneous rock flowed as lava onto the sea floor. Some of that igneous material forced itself between layers of limestone forming sills at an even later time. Today the igneous materials are evident as pillow lava formations (black basalt) in the Granite Park area, and as the Purcell Sill that runs through the Siyeh Limestone. A dark band of igneous rock (diorite) about 100 feet (30 m) thick, the heat of the intrusion recrystallized the surrounding limestone into white metaporphic marble.The Purcell Sill can be seen on Mt. Siyeh and Mt. Cleveland in Glacier, and Mt. Blakiston near Red Rock Canyon in Waterton.
[{"rock_types": "igneous", "era_formed": ["Proterozoic", "Proterozoic "]}, {"rock_types": "black basalt", "era_formed": "n/a"}]
[{"rock_types": "igneous", "era_formed": "Proterozoic"}, {"rock_types": "metasedimentary ", "era_formed": "Today"}] [{"rock_types": "igneous", "era_formed": "Proterozoic "}, {"rock_types": "black basalt", "era_formed": "n/a"}, {"rock_types": "Siyeh Limestone", "era_formed": "n/a"}, {"rock_types": "diorite", "era_formed": "n/a"}, {"rock_types": "white metaporphic marble", "era_formed": "n/a"}, {"rock_types": "Purcell Sill", "era_formed": "n/a"}] [{"rock_types": "Siyeh Limestone", "era_formed": "Proterozoic "}] [{"rock_types": "metasedimentary", "era_formed": "n/a"}, {"rock_types": "igneous", "era_formed": "Proterozoic"}, {"rock_types": "metaporphic", "era_formed": "n/a"}] [{"rock_types": "black basalt", "era_formed": "Proterozoic"}] [{"rock_types": "limestone ", "era_formed": "n/a"}, {"rock_types": "black basalt", "era_formed": "n/a"}]