282 | Transactions.— Geology. 
2. Stratigraphical Evidence.—The different varieties of rock pass gradually 
one into the other, no line of division extending beyond a few yards having 
been found, and по sequence of the different varieties can be traced, as can 
always be done among stratified rocks. I think, therefore, that all varieties 
of trachyte, porphyry, and breccia must be considered as belonging to one 
formation. Now this formation is spread over the greater part of the 
peninsula, and attains a height of 2,600 feet above the sea; and a closer 
examination of the district shows that the porphyries and other more 
metamorphosed varieties of the trachyte are found only towards its lower 
part, and do not extend up into the bills, as may be easily seen by examining 
the mines at various levels in the Karaka and Tararu Creeks, where meta- 
morphism has been most active. This cannot be due to decomposition of the 
upper portions, for near the base of the formation the rocks are quite hard in 
places where they have been exposed to the atmosphere for a long time, 
while higher up long drives into the hills show that the rock there has never 
been changed into a porphyry, for it contains no crystals nor crystal cavities, 
It is impossible to account for this fact on the supposition that the porphyries 
are older rocks tilted up, but it follows naturally from the supposition that the 
whole mass is of volcanie formation, which was ejected in a heated state ; for 
then the lower portions must have retained their heat longer than the upper, 
and, as the felspathie nature of the rock renders it very liable to meta- 
morphism, there is nothing extraordinary in finding the lower parts changed 
into a porphyry. 
Those districts which are most metamorphosed are also most brecciated, 
such as the Hape, Karaka, and Tararu Creeks, the beach north of the 
Opitomoko, and the country about Tapu. "This probably shows that the more 
metamorphosed districts were nearer to the volcanic vents, The absence of 
scoriæ is no argument against this view, for, as I have already said, the 
trachyte is more nearly allied to lava than to tuff, and it was certainly ejected 
below the sea, while scorie can only be formed in the air. I have already 
mentioned the great extent of country which this formation covers. This 
alone proves either that it is nearly horizontal, or that it is thrown into 
undulating curves. But the mines at the Thames have shown that it is crossed 
in all directions by nearly vertical dykes, which have no particular direction of 
dip in different localities, which would certainly be the case if the formation 
was thrown into undulating curves. At Coromandel seams of coal have been 
found at Sykes Gully, in the Kapanga township, and in the Hinau Creek, a 
small tributary of the Matawai.* In the first case the coal dips N.N.W. 15°, 
and in the second it is almost horizontal. In both places it is overlaid by 
* Both these beds of coal occur in the district marked as “ greenstone tufa forma- 
tion” in Dr. Hector’s map of Coromandel. (Geo. Rep., 1870-71, p. 98,) 
