Vol. 70.] LAYAS AT STOBTH HEAD, OTAGO HABBOUB. 



M07 



trachydolerite of the Siebengebirge type. The following analyses 

 enable vis to make a comparison between these rocks and other 



related types : — 



II. 



HI. 



IV. 



SiO, 56-85 54-48 50*50 40-40 



TiO", 1-20 1-01 0-40 



Al (.)., 21-56 14-71 17-64 20*46 



Fe~ O, * 3-44 5'68 5'41 5'72 



Feb 1-14 302 4*02 t'62 



Mg-0 0-85 2-10 3-33 1-68 



CaO 5-26 5-00 7-01 :>■ in 



Xa,0 6-07 6-13 5-52 5*81 



K..0 3-66 3-28 3-02 2'7G 



Los? on 



ignition 0-52 3-78 0'45 2-72 



, Totals... 90-35 00-08 00-71 00-03 



V. 



40-20 

 1 -42 



17-40 

 2-00 

 6-69 

 2-31 

 5-5fl 

 Q-7S 

 3-56 



4-40 



VI. 



VII. VIII. 



51-86 



10-87 

 6*30 

 3-11 



'2-33 

 3-77 

 6-20 



53-12 

 0-25 



20-48 

 513 



1-511 

 1-88 

 t-29 

 6-20 



i-ss 



1-00 2-25 



59-22 



1351 

 5' 55 

 |-(»: 

 1-66 

 5-13 

 5-31 



4,-64 



1-25 



00-31 100-31 00-08 100-38 



I. Laurvikite. Ttinsberg (Norway). H. Rosenbusch, 'Elemente dor 



Gesteinslehre ' 2nd ed. (1901) p. 114. No. 11. 

 II. Kaiwekite. Otago North Head. Dunedin (N.Z.). No. 13. 

 TIT. Easexiie. Rongstock (Bohemia). H. Rosenbusch, op. tit. p. 177. No. 3. 

 Trachydolerite. Otago North Head, Dunedin (N.Z.). No. 21. 

 Otago North Head. Dunedin (N.Z.). No. 21. 

 Leith Valley. Dunedin (N.Z.). Q. J. G. S. vol. Ixii 



IV. 



V. 



VI. 



Trachydolerite 

 Trachydolerite 

 (1906) p. 407 

 VII. Trachydolerite 



Bauza (Spain). II. 



Rosenbusch, ' 

 ( iesteinslehre * 2nd ed. (1901) p. 355. No. 3 a. 

 VITT. Andesite. Siehengelnrge. H. Rosenhusch. ibid. p. 300 



Elemente dev 



No. 



The relation of No. 13 to the laurvikite is quite marked, except 

 in the low percentage of alumina, which is explained by the greater 

 abundance of femic minerals. The kaiwekite in tins series is richer 

 in these substances than tie* St. Leonard's rock that was submitted 

 to Rosenbusch. 



No. 21 cv. Xo. 21. 0:1 the other hand, are undoubtedly traehv- 

 dolerites, although the mineralogical differences between them are 

 considerable. These differences are partly due to the complete 

 resorption of the hornblende in Xo. 21. The relatively high per- 

 centage of the alkalies in that rock accounts for the minerals nephe- 

 lineand sodalite, which are absent from No. 21. On the other hand, 

 there does not seem to be any close relation between the trachy- 

 dolerites and the Siebengebirge andesites, as suggested by Rosen- 

 busch. The close relation between these trachydolerites and those 

 of the Leith Valley, previously described, and also that of Bauza, 

 is clearly shown. That the trachydolerites are the volcanic repre- 

 sentatives of theessexites is shown by Analysis III. As previously 

 stated, the presence of barkevikite, violet augite, and olivine, and 

 the association of anorthoclase with a soda-lime felspar, strongly 

 support this conclusion. There is also in the Dunedin district 



Q.J.G.S Xo. 280 



2e 



