A small dyke of porphyritic microgranite which has " a dog's-leg shape " in plan was intruded into these rocks during the Devonian Period; this formed a plane of weakness which controlled the position of the fault.
12.
A second theory supposes that desert pavements form from the shrink / swell properties of the clay underneath the pavement; when precipitation is absorbed by clay it causes it to expand, and when it dries it cracks along planes of weakness.
13.
Soft ground drilling can be undertaken using a rotary auger or wash boring techniques, while rock drilling often use methods such as NMLC which allow for recovery of a core of material which can be examined to determine the strength, degree of weathering, understanding of any how intact the rock is ( RQD ) and identify any discontinuities or other planes of weakness.
