Tyndall stone, sedimentary rock, Manitoba. Formed in the Ordovician seas 450 million years ago. The mottles were formed by burrowing shrimps. Similar structures are formed in modern environments. The ghost shrimp makes tunnels and mounds that dot the shallow sea bottom in the Caribbean. Tyndall limestone is used as a decorative stone in the interior of the Parliament Building in Ottawa.The picture on the right is of a fossil called receptaculites which is found in Tyndall stone.