310 Essays. 



Coromandel Harbour and at Cape Colville, and tliere form tlie boundaries of 

 both sides of tbe Pritb of tbe 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 

 stratified like clay slate — (at Maraetai, on the Waitemata) . At other times 

 the siliceous element preponderates, and, from the admixture of oxide of iron, 

 the rock has a red jasper-like appearance (at Waiheke, Manganese Point), 

 In other localities it is more distinctly 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 Kew 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 Siliirian strata of Europe. In these rocks occur the cojjper 

 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 from the beds of quartz gravel in the 

 rivers and creeks flowing down from both sides of Coromandel range is 

 derived fi'om quartz veins, of crystalline 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 tuf£ and breccia, of which 

 the hills surrounding the Harbour of Coromandel are composed. The mag- 

 netic iron sand which, in washing, is f o and with the gold, is derived from 

 the same source as all the magnetic iron sand of JN'ew Zealand,t namely, 

 from the decomposition of trachytic 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 trachytic rocks, are quite different 

 from the auriferous qiiartz 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 Eiver, attaining 

 an altitude of 1,500 feet above the level of the sea — and striking from thence 



* Fischer's Translation, p. 14. 



t Magnetite occurs in the chloritic schists of Otago. — Ed. 



