"The banded or laminated structure in the Paleozoic schists of the South island, New Zealand, is shown to be a pseudo-stratification. The conclusion is reached that this banded structure is mainly the result of metamorphic differentiation, brought about by chemical mobilization of the more readily soluble constituents of the rock. In accordance with the theory of Sander, it is suggested that chemical mobilization reaches its maximum when mechanical action has reduced the grain size of the original rock so much that the velocity of the direct componental movement of grains, which is directly proportional to the grain size, is below a critical value. Supplemental influence of magmatically derived material, especially silica, is admitted but is considered subordinate. In many places the laminated structure of metamorphic origin has been transposed and partly obliterated as strong deformation continued."
Specimens of Yule marble deformed in extension by Dr. H. C. Heard at 400°-500° C., 5,000 bars, and strain rates between and . have been used for analysis of microscopic structure and fabric. The effect of lowering the strain rate a million-fold at 500° C. is broadly analogous to raising the temperature by 100° C. at constant rapid rate of strain. In all specimens the concept of statistically homogeneous stress in the strained material is supported by general correlation between the spacing index for e-twin lamellae and the resolved shear stress on the system of twin gliding. Turner's earlier dynamic interpretation of e-twinning in marble in terms of "compression" and "tension" axes is found valid if due account is taken of initial preferred oritentation of c-axes. Symmetry of c-axis orientation and of strain is consistently related to the combined symmetry of stress and initial fabric.
In a recent account of the petrography of certain low-grade, dynamically metamorphosed quartzo-feldspathic sediments from the Forbes Range, Western Otago, New Zealand, one of the writers x has noted the presence of a yellowish-brown strongly pleochroic mineral, which was identified as a ferruginous member of the stilpnomelane group.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
