GEOLOGY. 
97 
Where tlie conglomerate occurs, we find that the course of the 
river is always contracted, because those strata, strongly cemented 
by an argillo-arenaceous matrix, and consisting principally of 
rounded masses ol chert, hornstone, quartz, quartzite, jasper, 
sandstone, &c., have resisted much better than the soft sandstones 
and marls the erosion of the river. In many places we observe 
striking examples ot the degrading force of the river current, and 
how frequently nature employs only small means to produce great 
results. In the soft sandstones and clay marls near the bed of 
the river, large and perfectly circular holes are found, many feet 
deep, and having frequently a diameter of from five to eight feet, 
at the bottom of which lie rounded boulders of harder rock. 
During the freshes these boulders are put in motion by the 
whirling waters, and by their attrition every year make their 
abode broader and deeper. _ This tertiary formation, which is of 
the same age as the Motupipi brown coal (miocene P) is not only 
of great extent and elevation, but has also undergone considerable 
changes in its.stratigraphical position; for even admitting that the 
strata were originally deposited on the slopes of mountains beneath 
the sea, lying at a considerable angle, this could not have taken 
place at the angle of seventy-five or eighty degrees which they 
exhibit in some of the hills *in the Tutaki. We may therefore 
conclude that since their deposition they have not only been 
upheaved vertically to their present elevation, but that at the same 
time they were torn and rent in various directions, as exhibited 
by their present positions. As no tertiary strata appear to the 
west of the western range, the Lyell and Brunner ranges, &c., it 
is evident from this and for many other reasons, that the principal 
waters of the estuary alluded to came from the western side of the 
island, in which so many interesting changes have taken place, 
and that it was, in fact, formerly a mere extension of Blind Bay. 
This tertiary formation stretches as far south as Mount Mantell, 
where we meet it on both sides of the Matakitaki and the Maruia; 
it then disappears, and no other deposits cover the outcropping 
plutonic and metamorphic rocks than drift and alluvium. In the 
Matakitaki plains we again find tertiary strata covered by a large 
deposit of boulders, in some places 200 feet thick, below which 
layers of a greenish blue clay marl are visible, between which 
here and there occur small seams of lignite, which gradually thin 
out. 
I have already spoken of Mount Owen and its formation, and 
shall now proceed to observe upon the central chain of the island, 
lying on the western side of the longitudinal fissure, between it 
and the West Coast, and bounded on the north by the Mokihinui 
river, and on the west by the Grey plains. Although I traversed 
this chain I have not obtained such sections as I could have 
desired. In a few places only I found sedimentary rocks in situ, 
and the scarcity of our provisions just as we reached this central 
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