270 



CAPT. P. W. HUTTOI^ ON THE GEOLOGICAL POSITIOJf 



yellow or whitish arenaceous limestone with scattered green grains, 

 which get more abundant near the base but are never sufficiently nume- 

 rous to give it a green colour. The exposed surface is honeycombed, 

 thus strongly contrasting with that of the Amuri limestone. A close 

 inspection shows that the upper surface of the Amuri limestone is 

 much broken and fissured, the Weka-pass Stone penetrating into 

 the fissures for a distance of one or two feet, with an abrupt division 

 between the two rocks. Also rounded pebbles of the Amuri lime- 

 stone are found in the Weka-pass Stone within six inches of the 

 junction, but not higher. These pebbles are not concretions, as has 

 been supposed, for they are exactly similar in composition and 

 structure to the Amuri limestone on which the}' lie, and are quite 

 different in appearance from the concretions found in the green 

 sandstones underlying the Amuri limestone. Evidently we have a 

 waterworn surface, and therefore, as the nature of the upper 

 rock excludes the idea of chemical erosion, we have an uncon- 

 formity. In addition to this the Weka-pass Stone overlaps the 

 Arauri limestone to the north and rests on the slate rocks of Mt. 

 Alexander at Hurinui ; and as neither rock is a shallow water 

 deposit, and as the Amuri limestone extends far north of the 

 Hurinui, this overlap is another proof of unconformity. Over- 

 lapping is also seen in other places as mentioned in mj' report pre- 

 viously alluded to. 



Motunau River. — I have not examined this section myself, but 

 Mr, M'Kay says, that near the north-east part of Mt. Cass range 

 there is a syncline, in which the Grey Marl is seen overlying the 

 Amuri limestone (fig. 3). On the west side of this syncline the 



Fig. 3. — Section across the ^Soutli Branch of Motunau Creeh 

 {after M'Kay). 



For explanation see fig. 1. 



Grey Marl, containing here Pecten Zittelli *, rests unconformably on 

 the lower beds of the Waipara System, while it passes upwards 

 into the Mount-Brown bedsf, Nevertheless, Mr. M'Kay thinks 

 that this apparent relation of the Grey Marl to the Mount-Brown 

 beds is not real, because more to the north-east the Grey Marl is 

 interbedded with the upper portion of the Amuri limestone J ; 



* Pecten Zittelli, Huttou, is the same as the Pecten belonging to the group 

 Pleuronectes, in the palaeontology of the voyage of the ' Novara,' pi. ix. f. 3. 



t ' Geological Eeports,' 1879-80, p. 1 13. 



\ His section, however, shows the Grey marl as unconformable on the Amuri 

 limestone, as well as on the older Waipara beds (see fig. 3). and at 3a the 

 Amuri limestone is unconformable on the Waipara beds. 



