Final answer:
The relatively stable interior portion of a continent is known as a craton, which is a large stable block of the earth's crust that is the nucleus of a continent, such as the Canadian Shield in North America.
Step-by-step explanation:
The relatively stable interior portion of a continent is known as a craton. A craton is a large, stable block of the earth's crust forming the nucleus of a continent. For example, the Canadian Shield is part of the North American craton which has remained relatively stable and unchanged for millions of years. Such areas are often found in the central portions of continents and are composed mainly of ancient, Precambrian metamorphic and igneous rocks. Cratons can be covered by a thin layer of sedimentary rocks and are typically surrounded by younger, more deformed geological structures