110 
GEOLOGY. 
harbour being missing), or between the Cretaceous and Jurassic 
periods. The granite is here of a dark colour, and always con¬ 
tains large feldspar crystals, composing at times the greater 
portion of the rock. It continues for one mile towards the north, 
where this porphyritic structure disappears. 
Two miles south of the Potikohua stream, the cretaceous forma¬ 
tion again begins, but is here of a more argillaceous nature; 
brownish and bluish black interstratified clays, often from eighty 
to 100 feet thick, alternating with marls, and* containing the same 
fossils as before, accompanied by impressions of leaves and fossil 
shells allied to Cyrena. Included in these beds were here and 
there rounded pebbles of an older limestone formation, in all pro¬ 
bability underlying the coal formation, and full of fossils, of which 
I collected a good quantity. The strike of these extensive 
secondary strata is again nearly north and south, with a dip 
towards the west, varying between 9 degrees and 13 degrees. 
The large cave Te-ana-o-Matuku is hollowed out of granitic 
breccia, consisting partly of angular and partly of rounded 
boulders of granite, strongly cemented by granitic rubbish. 
This granitic breccia projects like a wall far into the sea, be¬ 
coming towards the east smaller and lower, and whilst the cre¬ 
taceous rocks on its western side have been washed away, on its 
eastern they still exist, and amongst them we lose all traces of it. 
In this breccia a rough stratification is visible, striking from 
north-west towards south-east, with a dip of 17 degrees towards the 
north-east. The cave itself runs from north to south, is seventy- 
five paces long, ten paces broad, and thirty feet high; from the 
middle another smaller branch runs towards the west, which is 
thirty-five paces long, and the entrance of which is washed by 
the sea. 
There is only one explanation to be given of this remarkable 
phenomenon, namely, that the detritus brought down by a torrent 
descending from a granitic mountain in the west, which has now 
disappeared, here entered a cretaceous sea, either in a bay or in 
the main sea, in which latter case the mountain probably stood on 
an island. The cave was afterwards excavated by the sea, which, 
during the slow upheaval of the present land, dashed, as it now 
does, furiously against the cliffs on its margin. In the bed of the 
river flowing near this cave, a great part of the boulders consists 
besides of granite gneiss and metamorphic rocks, of eklogite, a 
magnificent rock (consisting of grass-green smaragdite, red garnets, 
and silvery mica), and of grits, shales, and sandstones resembling 
those of the Davy mountains. 
A mile further on, the hypogene rocks again reach the coast; 
the granites become more trappean, and have everywhere in¬ 
truded into metamorphic schistose micaceous rocks (granulites 
and mica schists), either in large masses or in tortuous veins, 
affording to the observer ample opportunities for the study of the 
