Thomson. — Geology of Middle Waipara and. Weha Pass Disfricf . 353 



band " or "" layer." Since it is not always nodular within the district, 

 but is always more glauconitic than the overlying limestone, it is admissible 

 to name it the " Weka Pass greensand," and to confine the name of " Weka 

 Pass stone " to the overlying limestone. There are thus two greensand 

 horizons both in the Weka Pass and the Middle Waipara — viz., the Waipara 

 greensand below the Amuri limestone, and the Weka Pass greensand resting 

 on the Amuri limestone. There. is a third greensand horizon in the Waipara 

 River — viz., a facies of the "grey marls" resting on the Weka Pass stone. 



The Weka Pass stone is an arenaceous, slightly glauconitic limestone, 

 50 ft. to 100 ft. thick, the calcareous part of which is composed of the 

 tests of Foraminifera and a fine-grained base similar to that of the Amuri 

 limestone. In some parts, where the terrigenous elements are feebly 

 developed, the rock becomes almost indistinguishable from the Amuri 

 limestone, and, like it, is then thin-bedded and closely jointed, but for the 

 most part it is coarser in texture, is cream-coloured instead of white, and 

 is thick-bedded and not closely jointed. Consequently it presents, as Morgan 

 (1915) pointed out, a more massive appearance in natural exposures than 

 the Amuri limestone. Its chemical composition is shown in Table IV, con- 

 sisting mainly of 67 per cent, of carbonate of lime and 22 per cent, of silica, 

 whereas the Weka Pass greensand contains only 47 per cent, of carbonate of 

 lime and 35 per cent, of silica. The Weka Pass greensand, being a softer 

 rock than the two limestones it separates,, is generally hollowed out, and 

 the Weka Pass stone overhangs the hollow in a massive rounded ledge 

 (Plate XIX, fig. 1). Where the Amuri limestone below is also cliffed the 

 hollow of the greensand makes a marked break in the cliff, which is often 

 occupied by a sheep-walk. Along certain parts of the outcrop the Weka Pass 

 stone is apparently weaker towards erosion than the Amuri limestone, and 

 instead of overhanging it in a cliff, as is usually the case, forms a small cuesta 

 at the foot of the dip-slope of the more prominent Amuri limestone cuesta. 

 This is the case between Onepunga Farm (to the south of Boby's Creek) 

 and Mount Grey, and for a short distance north-east of the North Dean. 

 At Onepunga the Weka Pass stone is rather more glauconitic than usual, 

 and Speight and Wild have suggested that this and the greater abundance 

 of phosphatic nodules are evidence that the old shore-line is being approached. 

 More direct evidence would be an increase in the percentage and ^rain- 

 size oi the terrigenous material ; and, as this is wanting, the suggestion 

 lacks weight, more especially as the confirmatory evidence of overlap of 

 the lower beds is absent in this locality. 



The Weka Pass greensand presents two facies. In a few localities it is a 

 simple slightlv glauconitic calcareous sandstone presenting no peculiarities. 

 This is particularly the case in the middle part of the limestone clifis south of 

 the Waipara River, between the road leading down from the Ram Paddock 

 to the river and the limestone gorge. Lenticular masses of glauconitic 

 material appear in the upper part of the Amuri limestone, and these 

 gradually increase in number and size until the whole mass becomes 

 glauconitic, and after a few feet passes insensibly into the Weka pass stone. 

 At this locality " fucoids " are abundant in the upper part of the greensand 

 (Plate XIX, fig. 2), including a peculiar type with curved transverse divisions 

 like the septa of an Orthoceras, but unsymmetrical. 



Elsewhere the Weka Pass greensand presents a very peculiar contact 

 towards the Amuri limestone, a contact which has been repeatedh' claimed 

 as unconformable and with which a very considerable proportion of the 

 literature on the district has been concerned. \ Little can be added to the 



12— Trans. 



