438 Transactions. 



Miocene, and within late years between Park's Cretaceous and Miocene also. 

 Morgan, however, suggests that the rocks are of Eocene and Miocene age 

 respectively. Additional evidence consists very largely in the rediscovery 

 by Morgan* of a number of phosphatic nodules between the two rocks. 

 Wherever the two rocks occur the one rests on the other without any 

 change in dip or strike, and both are mainly foraminiferal. The phos- 

 phatic nodules are apparently regarded as rolled pebbles derived from some 

 phosphatic stratum, which, however, has never been located. It would 

 be much more reasonable to regard them as nodules formed on the sea-floor 

 in situ. It is well known that such nodules are of relatively common occur- 

 rence in dredgings from water of moderate depth. From the Agulhas 

 Bank several phosphatic nodules were dredged by the " Challenger "f 

 from depths of 98 and 150 fathoms. The form is capricious — generally 

 rounded, but also angular. The concretions from the shallower depths 

 were the larger (6 cm. in diameter) and contained much more glauconite, 

 and therefore possessed a green external appearance. The concretions are 

 said to be more abundant along coasts where there are great and rapid 

 changes of current, which cause frequent deaths of organisms. MerrillJ 

 states that it seems probable that Cretaceous and Tertiary deposits have 

 been formed under similar conditions in all parts of the world. Stutzer 

 also accepts the " Challenger " results as accounting for many phosphate 

 deposits. § F. W. Clarke, in the Data of Geochemistry, p. 104, describes the 

 methods of formation of such nodules. || 



It thus appears that the phosphatic nodules are probably original marine 

 deposits. Their occurrence implies rapid current changes, which are also 

 implied by the replacement of the Globigerina ooze of the Amuri limestone 

 by the arenaceous glauconitic limestone called the " Weka Pass stone " 

 that rests on it. The phosphatic nodules occur just where they would be 

 expected in a conformable rock succession deposited on a rising sea-floor. 



The gritty limestone of the Gibraltar Rocks is similar in most respects 

 to the hard bands in the hydraulic limestone in the Pahi Arm. As stated 

 by Marshall in the paper previously referred to, the limestone of the 

 Gibraltar Rocks consists mainly of Polyzoa, echinoderrn fragments, and 

 Foraminifera belonging to the following genera : Carpenteria, Globigerina, 

 Rotalia, and Amphistegina. At Colbeck's Landing the rock is mainly mud- 

 stone, but on the west side there is a band of gritty limestone which con- 

 tains many joints of stems of Pentacrinus. Some distance to the south-east 

 of the landing, at the point B (fig. 1), there is a thick mass of white limestone 

 with a highly crystalline appearance. This appearance is due to the abund- 

 ance of echinoderrn fragments, and with these there are a few Foraminifera, 

 mainly Globigerina. Some distance farther south, at C, there is some more 

 limestone much silicified and apparently brecciated. Close to it there is a 



* P. G. Morgan, Kith Ann. Rep. N.Z. Geol. Surv., Pari. Paper C.-2b, 1916, pp. 25, 26. 

 t J. Murray and A. Renard, Deep-sea Deposits, "Challenger" Reports, 1891, 



p. 391. 



\ G. P. Merrill, Non-metallic Minerals, New York, 1904, p. 264. 



§0. Stutzer, Uber Phosphatlagerstatten, Zeitschr. fiir prakt. Geol, vol. 19, 191b 

 p. 7. 



|| This has been stated definitely by Collet and Lee: "La glauconie et les con- 

 cretions phosphatees se forment actuellement sur le fond des mers. . . . Les concre- 

 tions phosphatees sont pour ainsi dire l'image du fond dans lequel on les rencontre ce 

 qui prouve bien leur formation in situ." (Recherches sur la Glauconie, Proc. Roy. Soc. 

 Edin., vol. 26, pt. 4, 1906, p. 266.) 



