IV. Summary: The Upper Triassic sediments are assumed to have contained concentrated solutions, which caused, or contributed to, their dehydration and contraction. The contraction of a colloidal mass results in the production of tension planes, and unless compensated by settlement, rupture finally ensues. Relief of pressure by rupture may bring the sohtions into the labile state, when innumerable closely-spaced centres of crystallization will be set up. The crystals, fed by vertically diffusing solutions, grow vertically, so long as contraction and feeding continue. When, at length, contraction attains its limit, further growth is resisted, and the stresses set up, transmitted to the central parting, produce bending and other pressure effects in the veins.