48-4 Transactions. — Geology. 



interesting one. It is said to be the one drawn by Major 

 Heaphy* to show the strata through which a vent is forced, 

 dipping down towards the vent. If it is the same, denudation 

 must have been very active, since the crater is gone and the 

 levels altered. I know, however, of no similar section in the 

 Auckland cliffs, and the blocks shown in Judd's " Volcanoes " 

 present much the appearance of the great blocks of Maitai 

 and Parnell grit and sandstone which have been emptied at 4, 

 or perhaps are the relics of the agglomerate in the old vol- 

 canic neck. 4 is the tuff. Numerous landslips have occurred 

 here, obscuring the relations between the more recent tuff and 

 the Waitemata beds. A plan of this tuff cone is given by 

 Hochstetter.f It forms a beautifully stratified cone, each 

 layer composed of basalt fragments in a clayey matrix ; and, 

 as already mentioned, the agglomerate of the old neck(?) con- 

 sists largely of green Maitai slates and phyllites often siliceous, 

 and Parnell grit. There can be no doubt that the basalt vent 

 burst through the grit. This forms a reef parallel to the 

 shore opposite the cone, and at A the reef has curved round 

 to the shore and dips up towards the cone. The chief interest 

 in the section, however, lies in the fact that here at last we 

 have the grit and the greensand together. But, unfortunately, 

 even here their relation is obscured. 



Near B the grit is quite white and crumbly, but weathers 

 in characteristic spheroidal fashion, so that it can easily be 

 recognised from below. Near A I am at a loss to account for 

 the appearance of the beds. Just below the grit is a sand- 

 stone, and the grit seems to lie unconformably on this sand- 

 stone, which is several feet thick at the first fault, and thins 

 quite out at the second. Stranger still, though the greensand 

 is lost at the fault, and, so far as I have seen, does not appear 

 below the grit towards B, at A the grit passes right over the 

 fault without any dislocation, and, rapidly increasing in dip to 

 over 50°, passes down to the sea round the head. The only 

 explanation I can give is that the eruption has driven the 

 harder bed over the softer ones for some distance. The ob- 

 jection to this supposition is that, although the appearance 

 in the section seems to fit in with it, just round A the grit 

 seems quite conformable to the underlying sandstone, which 

 in turn is only a few feet about the greensand. But I think 

 such a position for the grit impossible, for then at Orakei we 

 should see it above the greensand, while at Parnell we might 

 expect to see the greensand below the grit. As we do neither 

 there must be a considerable thickness of beds between them 

 — at least 50 ft., I should say — and the appearance beyond A 



* Judd : " Volcanoes," p. 1G5. 



f " Voyage of the ' Novara,' " vol. i., Geology. 



