IN THE LOWEE TERTIARY STRATA OP NEW ZEALAND. 179 



that the small quantity o£ carbonate of lime occasionally occurring 

 in the rock is due to the tests of these organisms. 



The general character and composition of this Oamaru siliceous 

 rock show a close resemblance to those pelagic deep-sea deposits 

 discovered by the ' Challenger ' Espedition, Avhich have been 

 described under the names of Diatom and Eadiolarian oozes. As 

 in these oozes, the Oamaru rock is largely made up of minute 

 organisms in varying proportions ; sometimes the diatoms pre- 

 ponderate, in others radiolariaus are abundant, whilst through- 

 out there is so considerable an admixture of sponge-spicules 

 that the rock might fairly be termed a sponge-bed. In the 

 recent oozes sponge-spicules also appear to be generally pre- 

 sent ; there is further, in the majority of these deep-sea de- 

 posits, a small number of foraminifera, and these organisms are 

 also present, but not in any great proportion, in some speci- 

 mens of the Oamaru rock, whilst ia others there are no traces 

 of them and the rock is wholly siliceous. The absence of coarse 

 arenaceous materials is the same in the Oamaru as in the recent 

 deep-sea ooze. We may therefore conclude that this Oamaru 

 rock was a deep-sea deposit, formed at some considerable dis- 

 tance from land, and that it may rightly be compared with 

 the Diatom ooze which now forms a belt of varying width sur- 

 rounding the South Polar Eegions, and extending from the 

 Antarctic Circle to about lat. 40° S. This recent Diatom ooze has 

 a range in depth of from 600 fathoms to 1975 fathoms, with an 

 average, according to the ' Challenger ' Eeport * lately issued, 

 of 1477 fathoms. The large proportion of radiolaria in some of 

 the Oamaru specimens may even indicate a greater depth than 

 that of a more distinct Diatom ooze ; and this supposition is to a 

 certain extent confirmed by the character of some ooze drt^dged 

 up by H.M.S. 'Egeria' from depths of 2479 and 3000 fathoms 

 in lat. 36° 53' S., long. 115° E., and lat. 36° 08' S., long. 117° 10' E., 

 respectively. This area is off the south-west coast of Aa-itralia. 

 In this ooze there are numerous detached sponge-spic iles with 

 radiolaria, and many of the former are closely allied to those from 

 Oamaru. 



There is a very great contrast between this siliceous Oamaru 



deposit and that which, according to the ' Challenger ' Ri-port' 



is now forming off the east coasts of New Zealand at depths of 



from 700 to 1100 fathoms. This recent deposit is a blue mud 



* Deep-Sea Deposits. 



13* 



