Folding of the rocks resulted from the operation of great compressive forces acting tangentially to the figure of the earth.
The safe tensile strength of Portland cement concrete would be something like one-tenth of its compressive strength, and might be far less.
It has considerable compressive or crushing strength, but is somewhat deficient in shearing strength, and distinctly weak in tensile or pulling strength.
Such composite structures take advantage at once of the high tensile strength of iron and of the high compressive strength of cement mortar.
On examining the diagram it will be observed that the maximum compressive stresses are parallel to and near to the down stream face of the section, which values are approximately equal to the maximum value of the vertical stress determined by the law of uniformly varying stress divided by the cosine squared of the angle between the vertical and the resultant.