226 The N.Z Journal of Science and Technology. [Nov. 
by a 100-mesh sieve were left in platinum vessels in contact with distilled 
water approximately at a temperature of 15° C. for six weeks. The solids 
dissolved during this period, expressed as percentages of the weight of the 
rock taken, were,— 
Silica (Si0 2 ) 
Alumina (A1 2 0 3 ) 
Iron oxide (Fe 2 0 3 ) 
Lime (CaO) .. 
Magnesia (MgO) 
Alkalis (by difference) 
(1) 
(2) 
(6) 
0-150 
0-120 
0-320 
0-014 
0-018 
0-018 
0-036 
o-oio 
0-160 
0-014 
0-008 
0-018 
0-008 
0-006 
0-008 
0*028 
0-014 
0-246 
Total solids dissolved (per cent.) .. 0*250 0T76 0770 
The Analyst remarks that “ the total amounts dissolved were very small, 
and the analyses of these must be taken as approximate only. They serve 
to show, however, that silica is the chief constituent dissolved, and that the 
ratio of dissolved iron to silica is higher than in the original rock. 
“ A further experiment indicated that the action of the river-water, 
which at this point contains only 7 grains of dissolved solids per gallon, 
would be similar to that of distilled water. 
“ Analyses were also made of a small deposit filling a vertical crack 
in a drive under the river-channel, and of a hard incrustation of the rock-face 
between flood-level and normal river-level.” The results were,— 
(1) 
(2) 
(3) 
(4) 
Silica (SiO 2 ) 
. . 41-76 
42-93 
59-20 
72-50 
Titanium dioxide (Ti0 2 ) 
0-22 
0-20 
0-04 
Alumina (A1 2 0 3 ) 
5-71 
319 
14-78 
9”12 
Iron oxide (Fe 2 0 3 ) .. 
. . 24-20 
28-91 
9-12 
3-84 
Lime(CaO) 
1-51 
3-35 
2-20 
1-20 
Magnesia (MgO) 
2'08 
2-84 
1-40 
0-39 
Soda (Na 2 0) 
0-83 
e 9 
3-56 
2-34 
Potash (K 2 0) 
0'67 
c 9 
2-32 
1-76 
Combined water and organic matter 
Water lost at 100° C. 
7-08 
.. 15-28 
18-32 
7-10 
8-60 
99-34 
99-54 
* 99-88 
99-70 
(1.) Dark buttery material in joint-crack. 
This is a hydrated silicate of 
iron and alumina 
resembling chloropal, a mineral of variable composition. One variety of chloropal 
of greenish colour, called “ pinguite,” is extremely soft, like new-made soap. 
Another variety has a dark liver-brown colour similar to the material here 
analysed. 
(2.) Chloropal from Mugrau.* 
(3.) Dark incrustation between normal and flood levels. It is impossible to obtain the 
thin incrustation free from adhering tuff. The Analyst remarks that the coating 
has the same general composition as the solids dissolved from the tuff by water, 
and was probably formed by deposition from water drying out of tuff on an 
exposed surface. 
(4.) Light-coloured incrustation on tuff between normal and flood levels. This was 
probably formed in a manner similar to No. 3. 
When the dam is built the river will be turned into an old channel formed 
when the stream flowed at a higher level. The northern end of this channel 
is cut for many chains in a somewhat weathered, fine-grained rock, harder 
and more compact than any of the pumiceous tuffs and breccias at the dam- 
site. This rock will prevent the river cutting back along the overflow channel 
to the spillway. In the field it was thought to be a flow rock, but under the 
microscope was seen to be a compact tuff. 
* J. D. Dana, System of Mineralogy, p. 701, 1904. 
