592 Transactions.— Geology. 
recognized at the White Cliffs, Taranaki, the upper end of the Manawatu 
Gorge, and doubtfully in the upper parts of the Wanganui and Rangitikei 
Rivers. In Hawke Bay and Auckland it is unknown. On the other 
hand, the Ahuriri formation is largely developed in the north from Cape 
Rodney and the Kawau, to Auckland and the Waikato. It occurs again 
largely between the East Cape and Napier, and all down the east coast 
of Wellington to the Wairarapa, and is found again on the west coast 
at Waitotara. In the South Island, on the contrary, it is only known 
in two limited localities, viz., the Hurunui Mound in the Nelson district, 
and the upper beds of Castle Hill Station on the Broken River, a branch of 
the Waimakariri. It would thus appear that the Pareora formation is 
almost entirely confined to the South Island, and the Ahuriri formation to 
the North Island, the two, as I have already stated, never yet having been 
observed in contact. Let us now see if this difference in geographical dis- 
tribution will in any way account for the difference in the fossils of the two 
groups of beds. 
Up to the present date 800 species of marine mollusca are known to 
inhabit our seas, and of these, 122, or 41 per cent., are only found north of 
latitude 42° S. ; 40, or 18 per cent., are only found south of that latitude ; 
while 138, or 46 per cent., are found both in the north and the south. The 
number common to both would, however, be much smaller if those Species 
had been omitted that are so rare either in the north or the south, that we 
could hardly expect that they would be found as fossils when the present 
sea bed becomes dryland. Nevertheless, we see that there is a considerable 
difference at present between the marine shells of the north and south of 
New Zealand. 
If, now, we arrange in the same way, the 179 species of fossil shells 
found in the Ahuriri and Pareora formations, we find that 41, or 23 per 
cent., are found only in the north ; 82, or 46 per cent., are found only in 
the south ; while 56, or 31 per cent., are common to both north and south. 
We see, therefore, that the difference in the Ahuriri and Pareora formations 
is considerably greater than the present difference, and we should not, I 
think, be justified in supposing that the difference between the fossils of the 
Ahuriri and Pareora formations was caused altogether by their different 
geographical distribution, although probably a certain amount of influence 
may be attached to it. ; 
Difference in station.—Turning now to the other possible cause, we find 
‘that in all the localities for Ahuriri fossils the rocks are more or less cal- 
careous, while in all the localities for Pareora fossils the rocks are either 
clay or sandy clay, with the exception of Mount Caverhill, Lyndon, and 
Mount Cookson in the southern part of the district of Nelson, Here, 
