The Laurentides are of either late Cretaceous or later age. They are too much eroded to be of late Tertiary age. It was the Shield that was elevated and not the Cadian ones. The water of the St. Lawrence is muddy in port Quebec and all the way to north of the island of Orleans. It keeps up farther north but the more pure salt water gets to Orleans. At about 46 miles N.E. of Quebec the water is practically free of mud and is more transparent. In other miles practically all of the St. Lawrence mud is deposited in less than 40 miles due to the influence of the salt water.