_The Laurentian Highlands._--A vast area in the eastern portion of Canada, to the north of the valley of the St. Lawrence, including Labrador, is underlaid by very ancient crystalline rocks of the same general character as those forming the Adirondacks. This same geological system, the Archean, has a wide development in the continental basin to the north of Lake Superior and about Hudson Bay. To the north of Quebec, in the region drained by the Saguenay and Ottawa Rivers, the land has a general elevation of 1,500 to 1,600 feet, and is known as the Laurentian Highlands, although sometimes dignified by the name Laurentian Mountains, or, more briefly, as the Laurentides. In reality, this broad, indefinitely defined region from a geographical point of view is a roughened plateau and not a mountain range or group of ranges. When the structure and metamorphosed condition of the rocks are considered, however, it is found that they have the characteristics pertaining to the central and more deeply seated portions of true mountains. The rocks are mainly crystalline schist, gneiss, granite, etc., together with igneous intrusions, all of which have been intensely folded, crumpled, and broken. The general interpretation of the existing conditions is that deep erosion has occurred and, in fact, a mountain range or a mountain chain worn down to a generally plane surface. The thickness of the rocks thus removed, or the depth of erosion, is unknown, and owing mainly to the complexity of the geological structure of the terranes remaining, will perhaps never be ascertained, but can be safely estimated as not only hundreds, but several thousands of feet. Erosion has laid bare portions of the earth's crust which were once deeply buried, and reveals the character of the "basement complex," as it has been termed, which forms the foundation of the continent. Owing to the great age of the rocks and the depth to which they were once depressed in the earth's crust, they have experienced great changes. They are not only intensely folded and crushed, but in large part have been caused to flow under great pressure, and have thus acquired a schistose structure. Fissures have been filled with molten rock injected from below so as to form dikes, and possibly still greater or regional intrusions have occurred. Over large areas the amount of once molten and intruded rock exceeds the surface exposure of what are usually, but with some hesitation, classed as metamorphosed sediments.