As the name suggests, volcanic mountains are formed by volcanoes. Volcanic Mountains are formed when molten rock (magma) deep within the earth, erupts, and piles upon the surface. Magna is called lava when it breaks through the earth's crust. When the ash and lava cools, it builds a cone of rock. Rock and lava pile up, layer on top of layer.
Fold mountains are mountains that form mainly by the effects of folding on layers within the upper part of the Earth's crust.
In the time before either plate tectonic theory developed, or the internal architecture of thrust belts became well understood,
The term was used for most mountain belts, such as the Himalayas.