Synclines, Anticlines and Overthrusts - How Compression Folds Rock Into Mountain

Using two paperback books as a prop, Randall walks through the sequence of structures that compressional forces produce in rock strata. When two sections of crust are squeezed together, the layers - think of the pages as geological strata - begin to deform in predictable ways. The first result is a monocline, a single inclined layer. As compression increases, the strata fold into a syncline - a downward curve - and an anticline, an upward arch. Push further still and the folded rock begins to slide, producing an overthrust - where one section of crust rides up and over another along a fault plane.

The Canadian Rockies, Randall notes, are among the most magnificent examples of overthrust mountain building on Earth. What appears from a distance to be a straightforward mountain range is in geological reality a stack of rock sheets that have been compressed, folded, and driven horizontally over one another across distances that can stretch for hundreds of kilometres - the accumulated result of the same compressional forces that can be demonstrated, in miniature, with two paperback books on a table.