76 
Keith R. Miles. 
In addition to the quartz, nodule A contains a number of clearly visible 
sub-angular fragments of creamy white colour showing cleavage faces charac- 
teristic of felspar. These reach up to 3 mm. in diameter. 
Broken faces of nodtiles C, D. and E occasionally contain small cellular 
surfaces stained yellow with iron oxide. 
Micro. — Apart from the detrital quartz and occasional felspar visible in 
hand specimens as already mentioned, other essential constituents which can 
be recognised under the microscope are grains of glauconite and iron ore en- 
closed in a matrix or cement of light yellow-brown coloured amorphous isotropic 
material with refractive index distinctly > quartz (about 1*6), which is 
identified as collophanite (or collophane). In addition, in many of the slices 
there are small fragments of phosphatised wood in which the original cell 
structure is often perfectly preserved but which are now composed entirely 
of collophanite. The microscopic appearance of typical thin slices is shown 
in Text fig. 1. 
The quartz grains are usually clear and vary from sub-angular and occas- 
ionally sharply angular for the smaller grains, to distinctly rounded for the 
larger grains. A rapid microscopic survey suggests that in nodules con- 
taining quartz grains of the same average grain size the degree of rounding 
is about the same. 
Detrital felspar grains were found to be most abundant in nodule A, 
(Text fig. 1A) but were present in all specimens examined. They consist 
mainly of mi 'crocline showing typical cross hatched twinning, but a few grains 
of untwinned orthoclase were recognised. In nodule A both microcline and 
orthoclase occasionally showed incipient kaolinisation and alteration to pale 
green chlorite. In nodules B, C, D, and E and to a lesser extent in A, many 
of the felspar grains showed considerable alteration and replacement along 
cleavages, to a yellow-green mineral displaying aggregate polarization, which 
is indistinguishable from the glauconite. 
Glauconite is present in varying amount in all specimens. It occurs in 
irregular shaped rounded pellets or granules ranging in colour from yellow- 
green to olive green and in size from about 0 03 mm. up to approximately 
0*4 mm. diameter (see text fig. 1A and B). These have refractive indices 
ranging from slightly less than to distinctly greater than that of the enclosing 
collophanite. They show aggregate polarization, the interference colours being 
almost entirely masked by the absorption colour of the mineral. No inter- 
ference figure was obtainable. In several of the nodules, especially in D and 
E. some of the glauconite showed partial alteration to limonite. Occasionally 
glauconite granules were seen to enclose minute fragments of black opaque 
iron ore. The glauconite granules usually occur in scattered groups surrounded 
by collophanite. 
The iron ore occurs in two forms — in sporadically scattered, usually 
rounded (detrital) black opaque grains ranging from about 0*02 mm. to 0*20 
mm. in diameter, and as red opaque filling material found in places 
rimming grains of glauconite, quartz and black iron ore, and occurring in 
occasional veinlets traversing the slices. 
Examination of the black opaque grains obtained from crushed nodule 
material showed that some of these were distinctly magnetic and many others 
non-magnetic and on crushing yield a red powder — thus it is probably mostly 
hematite with some magnetite — nearly all grains being altered in some degree 
at least, to limonite. 
