178 DR. HINDE AND MR. HOLMES ON SPOIfGE-REMAINS 



Cave Valley, and Jackson's paddock and Bain's farm in the adjoin- 

 ing "WaiarekeiValle_y, about fourmiles from Oamaru. At Jackson's 

 paddock the beds have a thickness of from 40 to 60 feet. They 

 are immediately overlain by the v\'ell-known Ototara limestone, 

 and they rest on beds of volcanic rock. In some places also the 

 deposit is traversed by volcanic dykes, which have had the effect 

 of hardening and partially fusing the siliceous material in their 

 vicinity. There is some difference of opinion amongst New 

 Zealand geologists as to the relative age of this Ototara limestone 

 and the siliceous beds beneath it. By Sir Jas. Hector, E.E.S. *, 

 they are considered to be of Cretaceo-Tertiary age, about the 

 horizon of the Lower Eocene ; Capt. Hutton f, on the other 

 hand, places them in the Upper Eocene or Oligocene, and this 

 latter view is probably approximately correct. 



In general appearance the specimens of this Oamaru material 

 which have been sent to this country very much resemble our 

 Upper White Chalk ; they are, when dry, of a greyish-white tint, 

 soft, earthy, friable, and readily breaking up into a fine mud of a 

 creamy tint in water. Unlike the chalk, however, most of the 

 specimens appear to be entirely siliceous, and show no reaction with 

 acid, but in some there is a small proportion of calcareous material. 

 In the rock unaltered by heat, the different kinds of microscopic 

 organisms of which it is composed are heterogeneously intermingled 

 together, and the individual forms are either entirely free from 

 each other, or lightly cemented by an impalpably fine material 

 formed mainly by the comminuted skeletal debris of the diatoms 

 and radiolarians, so that by careful manipulation these organisms 

 maybe obtained free from matrix. The deposit seems to be 

 nearly wholly of organic origin ; no sand or other coarse materials 

 of mechanical derivation can be distinguished in it. The distri- 

 bution of the different kinds of organisms is by no means uniform 

 throughout the deposit, for while some specimens consist chiefly 

 of diatoms with a few radiolaria and the minuter forms of 

 sponge-spicules, in others the spicules are relatively large and 

 there is only a slight admixture of diatoms. It has also been 

 noticed tl)at certain genera of diatoms are abundant in some 

 portions of the rock and very rare in others. In the partially 

 calcareous portions, foraminifera are also present, and it is evident 



* Keport 1876-7 Geological Survey of New Zealand, pp. iv, 48, 

 t Geology of Otago, 1875, p. 54. 



