458 
THE GEOLOGY OE NEW ZEALAND. 
This leads to the consideration of sedimentary deposits; 
these are chiefly marine or lacustrine, the first are formed 
in the way already mentioned, and the shoal seas around a 
great portion of these islands mark their extent. On the 
western coast of the North Island, it is evident vast tracts 
of land have been gained from the sea, by the deposits of 
the Wanganui, Rangitikei, and Manawatu rivers ; near the 
coast, in that part, the land is generally low, covered with 
gravel or shingle, and large quantities of drift timber ; inland 
it is alternate swamp and grass with parallel ranges of ancient 
sand hills covered with a growth of fern, formed by the 
inroads of the sea on those coasts ; near the sea, and espe- 
cially at the mouth of rivers, large quantities of sand are 
blown up from the shore, and form drifting sand hills ; the 
mud being precipitated to the bottom of the sea by the coagu- 
lating action of salt water, there gradually forms a compact 
mass : but the sand having nothing to fix it, is by constant 
attrition washed finer and finer, and then thrown up by the 
high tides in large quantities on the shore, whence the sea 
breeze speedily conveys it inland. 
The valleys of New Zealand are not numerous or exten- 
sive ; indeed the almost entire absence of them, and the 
acute pointed hills, which are only separated from each other 
by deep ravines, are to be considered as amongst the pecu- 
liar features of the country, and as most of these have never 
been touched by the hand of man, they enable the Geologist 
to discern the exact state they were in when first upheaved ; 
the remarkable way in which the surface of these islands 
was fractured when first elevated, is yet to be observed 
as plainly as though it had recently taken place ; for whilst 
one side of a hill is covered with the debris of primitive 
rocks, gravel, and vegetable mould, the other is either ochre 
or pipe clay, destitute of any rolled stone, and without soil ; 
the fern also on one side is of a more luxuriant growth than 
on the other.* 
Another kind of deposit remains to be noticed, the vol- 
canic. Wherever a volcano has arisen in the sea, or its 
* The country is cracked at an angle of 45 °. 
