The Silurian strata seen at Siccar Point were deposited by turbidity currents flowing down the continental slope into the trench. The following sequence of diagrams shows how they rotated from their original horizontal orientation to their now nearly vertical orientation.
Stage 1: Strata are laid down in approximately horizontal layers
Stage 2: The strata start to rotate as they are dragged down by the subduction process.
Stage 3: The strata are rotated until they are nearly vertical.
In the steeply dipping Silurian strata you should look for way-up criteria such as graded bedding or ripples produced by flowing currents.