1. Not all rocks are suitable for the studies
The suitable rocks are:
Sand stones and shales – Sedimentary rock
Gneissses and schist ( to some extent) - Metamorphic rock

2. Folds
They bend either upwards or down wards when a set of horizontal layers are subjected to compressive forces
Parts of fold:
Limbs or flanks - side of a fold
Crest and trough – the curved portions of fold at the top and bottom are called crest and trough respectively
Axial plane- Imaginary plane which divides the fold intotwo equal or nearly equal halves’
Axis – Trace of intersection between the axialplane and the crest or trough of the fold
Wave length – The distance between the successive crest or trough

3. Classifications and types of folds
Based on different principles the folds are variously classified as
Symmmetrical and asymmetrical – symmetrical character
Anticline and syncline – upward or downward bend
Occurence of plunge – plunging and non-plunging
Uniformity of bend thickness – open and closed
Behaviour of the fold pattern with depth – similar and parellel