468 



Transactions. — Geology. 



At Tamaki West Head, in the tuff (or volcanic neck ?) 

 of another basalt puy, large angular blocks of Maitai 

 slates, quartzites, and phyllites occur. Lumps of Parnell 

 grit have also been ejected. Some of the Maitai blocks 

 are several feet in diameter, and the rocks must be quite 

 close in situ. Farther east Motutapu is an island con- 

 sisting mainly of Maitai slates. Much to the west, near the 

 south head of the Manukau Harbour, Maitai slates have also 

 been found. These points may be connected by an almost 

 straight line, and, bearing in mind the lithological evidence 

 and the fact that the Cheltenham breccia seems never to have 

 passed this line, it seems reasonable to infer that in Oligocene 

 times there existed a Palaeozoic ridge or chain of islands, 

 whose sunken summits are still traceable, which acted as a 

 barrier to the western deposits. In Lower Miocene times it 

 had sunk beneath the sea, and the Parnell grit spread over 

 the whole area. 



The fossil evidence for an Oligocene age is strong. The 

 forms appear to me to represent a position somewhat inter- 

 mediate between the Orakei green sand and the Papakura 

 limestone ; but, as the conditions were somewhat different, 

 the Cheltenham breccia and Papakura limestone may really 

 be contemporaneous. Below I give a list of the fossils 

 so far obtained from the beds. Those marked with an " x " 

 have not hitherto been named as occurring in them. I have 

 not given in full the list of Foraminifera from Orakei, because 

 the Cheltenham forms were not distinct enough to warrant 

 identification. The Barnea from the Cheltenham bed I could 

 not identify, nor was the Orakei Barnea identified by Mr. 

 Park. 



