Cnawronp.— Geology of the North Island of New Zealand. 307 
island) to the northward and eastward of a line struck from the southern 
slopes of Mount Egmont and Ruapehu, and are broken through by volcanic 
rocks, which, to a considerable extent, overspread their surface. 
. The secondary or mesozoie rocks as yet discovered or positively known 
occupy an area of moderate extent, and the greater part of the surface of 
the island is covered by the above strata of tertiary age, both sedimentary 
and voleanie. 
Before entering upon a description of the palmozoie rocks, it is however 
necessary to state that there is reason to suspect that a considerable pro- 
portion of the rocks now classed as paleozoic may have hereafter to be 
transferred to the mesozoie list. Dr. Hector thinks that the sandstones and 
slates associated with the plant beds near Wellington have a strong 
resemblanee to mesozoie rocks elsewhere in New Zealand, and that they will 
probably be found to lie unconformably upon the older diorite rocks of the 
neighbourhood; while I have a decided impression that the rocks of the 
ranges at Cape Palliser will prove to be of later date than those of the 
Rimutaka Range on the eastern side of the Wairarapa. With the above 
understanding, it will be as well, for present purposes of deseription, to 
consider all the apparently old and highly inclined rocks of the great leading’ 
ranges of mountains as of palæozoic age. 
Primary og Panxzozorc Rocks. 
There is reason to suppose that the palwozoic rocks, which are almost 
invariably found highly inclined, decrease in geological age from west to 
east. They appear to have been subjected during the lapse of ages to 
extreme lateral pressure, which has thrown them, partieularly towards the 
eastern or main ranges, into abrupt mountain ridges, extending in a N.N.E. 
and 8.5. W. direction, and enclosing only very narrow valleys. Except where 
these mountain ridges rise from out of the tertiary covering, the indication 
of their existence can often only be proved at remote spots, where the 
violent torrents near the sources of the great rivers have scooped out deep 
gullies in the soft tertiaries, and left a flooring of old slates or sandstones 
exposed in their beds. ! 
Although the voleanie chain of Ruapehu and Tongariro may be said to 
be the leading feature of the North Island, rising as it does from a very 
elevated plateau, one of its cones, Ruapehu, being the highest mountain in 
the island, yet we cannot consider this isolated chain as the leading range, 
but must award a higher structural importance to the palwozoie ranges 
further to the eastward. These ranges, though broken, pass completely 
through the island from the coast near Wellington in a N.N.E. direction. 
They haye an extreme width of about twenty-three miles, and a minimum 
