I 
, GEOLOdY. 103 
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4 feet lignite, often very fissile. 
3 feet slate clays. 
3 | feet lignite. 
4£ feet clays, gradually becoming more ferruginous, and ultimately changing 
into loam and drift, which last was at least forty feet thick. 
The strike of these beds was from north-north-west to south- 
south-east, with a dip towards the east-north-east of 28 degrees. 
Near the junction of the Mawhera-iti with the Grey, on the 
southern side of the main river, I obtained another section. Here 
the banks are almost vertical, exposing a section of nearly 120 
feet. In the river itself we find a large stratum of clay marl, in 
which are also many pieces of driftwood converted into lignite. 
These beds, of a bluish colour, are nearly horizontal, and at one 
place the stump of a tree, fifteen inches in diameter, broken off 
about two feet above the root, stands apparently in situ, the roots 
still adhering strongly to the clay marls, so as to lead to the in¬ 
ference that it grew upon the spot. These beds, which rise nine 
feet above the level of the river, were probably deposited in a 
shallow estuary ; they are divided at irregular intervals by hori¬ 
zontally-deposited layers of mica; they change insensibly into 
loam, which is succeeded by a large accumulation of sand, gravel, 
and loam, interstratified with layers of boulders, partly angular 
and partly rounded, and resembling very much the drift formation 
near Nelson. 
At the western side of the Grey plains a succession of ferru¬ 
ginous clays, thirty feet thick, occur, over which again the drift 
formation appears. The rivers running through them have formed 
several terraces, which, near the mountains, attain an altitude of 
200 feet, whilst in the central part of the plains there is only one 
terrace from 100 to 120 feet in height, bounding the lower 
grounds near the river. A glance at the geological map shows 
that these large tracts of level land were formed before the ter¬ 
tiary period, and that the Buller emptied itself into an arm of the 
sea, which then occupied the space now included by these plains, 
into which the Inangahua, the Grey, the Aliaura, &c., also dis¬ 
charged themselves. During the sinking of the country in the 
glacial period the valley was filled up, and when the island rose 
again, an insurmountable obstacle was probably presented to the 
southern flow of the Duller, partly by the accumulation of drift 
during that period, and partly by the depression caused by the 
tilting (so to speak) of the whole country from south to north. 
A depression in the western chain, worked out either by sea 
currents or by rivers descending from it, at the same time offered 
to the Buller its present exit for its waters. This theory is con¬ 
firmed by the fact that in the Buller valley, between the Paparoha 
and Papahaua chains, no drift is found having the least resem¬ 
blance to that seen on the banks of the river flowing through the 
plains. 
