310 Essays. 
Coromandel Harbour and at Cape Colville, and there form the boundaries of 
both sides of the Frith of the Thames. For a description of these rocks we 
must-refer to Hochstetter, who writes as follows* :— 
“The oldest rock I have met with in the Province of Auckland belongs 
to the primary formation. It is of very variable character, sometimes being 
more argillaceous, of a dark blue colour (when decomposed, yellowish brown, 
the colour generally presented on the surface), and more or less distinctly 
apatites like olay sigle. 108 Maraetai, on the Waitemata). At other times 
1 ,and, from the admixture of oxide of iron, 
the rock has a red Fai. appearance (at Waiheke, Manganese Point). 
In other localities it is more distinetly arenaceous, resembling the old sand- 
stones of the Silurian and Devonian systems, called grauwacke (at Taupo, 
on the Hauraki Gulf). As no fossils have yet been found in this formation 
in New Zealand, it is impossible to state the exact age. I am, however, of 
opinion that these argillaceous siliceous rocks will be found to correspond 
to the oldest Silurian strata of Europe. In these rocks occur the copper 
pyrites, which has been worked for some years at the Kawau and Great 
Barrier, the manganese (psilomelane) at Waiheke, and the gold-bearing 
quartz at Coromandel. 
*'The gold which is washed out Pes the beds of quartz gravel in the 
rivers and creeks flowing down from both sides of Coromandel range is 
derived from quartz veins, of erystalline character and considerable thickness, 
running in a general direction from north to south, through the old primary 
rocks, which form the foundation of the Coromandel range. In some places 
these veins stand up like a wall on the summit of the range to the height of 
eight or ten feet. The clay slate rock itself is exposed only at the bottom of 
deep gorges which form the channels of the principal streams. In almost 
all places it is covered by large masses of trachytic tuff and breccia, of which 
the hills surrounding the Harbour of Coromandel are composed. The mag- 
netic iron sand which, in washing, is found with the gold, is derived from 
the same source as all the magnetic iron sand of New Zealand,t namely, 
from the decomposition of trachytie rocks. Small veins of quartz of amor- 
phous character—that is, not crystalline, but in the shape of chalcedony, 
carnelian, agate, and jasper—are found in numerous places on the shores of 
Coromandel. These veins, occurring in trachytie rocks, are quite different 
from the auriferous quartz veins in the primary formation." 
“The primary formation occurs, to a more considerable extent, to the 
eastward of Auckland, in ranges on both sides of the Wairoa River, attaining 
an altitude of 1,500 feet above the level of the sea—and striking from thence 
: es Translation, p. 14. 
. T Magne ret C 
Eds xii. Wn 
^ Qr Otago. 44D, 
Ler 
