Grange. — Geology of Green Island Coalfield. 



161 



sea. They have been cut out of the glauconitic mudstone, and are in an 

 excellent state of preservation. A few chains to the east of the Saddle 

 Hill railway-bridge over Abbott's Creek a cutting exposes slightly con- 

 solidated sand, as much as 15 ft. above sea-level, resting on a green-coloured 

 mud which contains a few fresh-looking sea-shells. At about the 200 ft. 

 contour-line in the Abbotsford Valley, and to the north of Green Island 

 Station, the country takes on a mature form that is lost at a lower level. 



This break in topography is independent of structure. Evidently, then, 

 the sea at one time stood 15 ft., and at another 100 ft. above its present 

 level, but good evidence is wanting to determine the sequence of the 

 diastrophic events. The freshness of the 15 ft. terraces suggest that an 

 elevation of that amount took place after the depression. 



GENERAL GEOLOGY. 

 The following table shows the classification adopted :- 



TRIASSIC FORMATION. 



This rock forms the Chain Hills. The junction of schist and Tertiary 

 rocks near Freeman's colliery occurs along Fernhill Creek. Farther south 

 a bluff of rock extends from the Chain Hills into the valley in which are 

 situated the Saddle Hill mines. This mass of metamorphic rock extends south 

 along the hills forming the southern border of Taieri Plains to Otakaia. 



The schist is not as completely metamorphosed as that of Central Otago. 

 There is not the frequent lamination of quartz and mica. Thin sections 

 show muscovite, feldspar (albite), and quartz. Dolomite is occasionally 

 found occupying small cavities. The dip of the formation varies. In the 

 railway-cuttings on the east side of the tunnel the following dips were 

 obtained : 20° to the south-east, 40° to the south-east, and 70° to the 

 south-west. Near the lower entrance to Freeman's mine the beds are 

 almost horizontal. A quartz reef 7 ft. wide, and striking 14° south-east, 

 outcrops on the schist spur projecting towards Christie's Creek. 



Diverse opinions have been held as to the age of the schists of Otago : 

 Marshall (1918, p. 29) ; Trechmann (1918, p. 171). Provisionally the rocks 

 of Chain Hills which show a similarity to those of Lawrence (Marshall, 1918, 

 p. 29) may on the same grounds be placed "in the Triassic. 



6 — Trans. 



