oil on canvas,
50cm x 50cm,
Iain White, 2016,
This painting is representative of one of the outcomes of Cadell’s hardware model experiments in structural geology. This result approximates to what many geologists today believe. This view which Cadell himself favoured maintains that duplexes form in a simple way, one thrust at a time. The idea is that each new thrust is formed ahead (in the so-called "footwall") to the previously active thrust. In this way earlier formed structures are bulged up and carried by the later ones moving below. The term "piggy-back" thrusting has been coined for this type of behaviour.
However, other geologists have suggested that duplexes are formed in a reverse order so that higher thrusts have moved later. In this way the upper thrusts should truncate the underlying ones, decapitating the underlying structures. The geometry is sometime described as showing "overstep". This was the model preferred by John Horne.
The debate has swung back and forth ever since. It seems likely that both styles can happen depending on which parts of the Moine Thrust Belt one considers.