Speight and Wild. — Weka Pass Stone and Amuri Limestone. 69 



The Nodular Layer. 



This layer is most important, as giving some idea of the conditions 

 which obtained in the interval between the deposit of the two limestones, 

 and therefore it will be described in detail. The most important constituent 

 in point of volume is a calcareous greensand which fills borings in the upper 

 surface of the Amuri limestone and passes up into the overlying Weka 

 Pass stone, the lower parts of which are decidedly glauconitic, and there is 

 apparently no pronounced line of division between them. Included in this 

 matrix of greensand are numerous nodules which are more or less phos- 

 phatic, so that it may be called the phosphatic nodule bed. This nodular 

 material is of two kinds — (1) true phosphatic nodules, and (2) nodular 

 masses of Amuri limestone. 



Phosphatic Nodules. — The descriptions of similar nodules occurring in 

 deep water south of the Cape of Good Hope, on the Agulhas Bank, 

 as given in the reports of the " Challenger " Expedition (" Deep-sea De- 

 posits," p. 396) applies so exactly that we can use the same words to 

 describe appropriately those occurring in our own limestones. The descrip- 

 tion is as follows : " The concretions vary from 1 to 3 cm. in greatest dia- 

 meter ; exceptionally they may attain from 4 to 6 cm. in diameter. They 

 are surmounted by protuberances, penetrated by more or less profound 

 perforations, and have on the whole a capricious form, being sometimes 

 mamillated with rounded contours and at others angular. Their surface 

 has generally a glazed appearance and is usually covered with a thin dirty 

 brown coating, a discoloration due to the oxides of iron and manganese." 

 The description further points out that grains of glauconite form a notable 

 constituent in their composition, and especially is this the case in those 

 from shallower water, which are larger and have a greenish-coloured external 

 appearance. This is important, as the great majority of those found in 

 the limestones have a greenish-coloured external appearance. The con- 

 cretions are described as being hard and tenacious, " the fundamental mass, 

 in spite of its earthy aspect, being compact, and having a hardness that 

 does not exceed 5." This description so fits the nodules in the greensand 

 layer that one cannot help suspecting a similarity of origin in the two cases. 



For the purpose of comparison of the chemical composition we quote 

 three analyses — the first, of one of the Agulhas Bank nodules ; the second, 

 one cited by McKay (1887, p. 84), of a nodule from the greensand layer at 

 the Weka Pass ; the third, of a nodule collected by us at Boundary Creek. 



It is unfortunate that the second and third analyses are not more com- 

 plete, but the general similarity of the results obtained will be noted. 



The nodules from deeper water, as pointed out subsequently in the 

 report (p. 393), differ from those just referred to, and the same applies 



