Serpentine, Lanark marble, metamorphic rock. This is metamorphic rock which was originally limestone with sandy layers. The rock was transformed by heat and pressure into marble. The green layers formed where the quartz sand occurred. This rock was the first decorative building stone to be mined in Ontario. It was used in building Rideau Hall, Ottawa. The building of Rideau Hall was started by Thomas MacKinnan, a Scottish stone mason and industrialist in 1826. He was the contractor for the Rideau Canal. The hall was purchased by the government in 1869 to be used as a residence for the Governor General.