162 Transactions. 



NOTOCENE SEDIMENTARIES. 



PlRIPAUAN. 



Rocks of the Piripauan group crop out along a narrow strip which, from 

 near the junction of North Taieri and Abbott's Hill Road, follows Fernhill 

 Creek, then Abbott's Creek to Samson's and Loudon's mines, crosses the 

 Main South Road, and bends round the bluff of schist near Christie's Creek. 

 Isolated outcrops occur on either side of the valley leading north from 

 the Brighton Creamery. The downward succession is : Shelly limestone 

 (absent from Fernhill outcrop), quartz sands, coal-measures. 



Coal-measures. 



The coal-measures are composed of quartz sands, fireclay, shales, and 

 seams of coal. Generally six seams of coal are present. The seam above 

 the lowest is the thickest, and is the only one worked. 



The coal is close to the schist, so that it is only natural that there will 

 be considerable differences in the thickness of strata below the main seam. 



The thickness of the coal-measures is between 100 ft. and 140 ft. The 

 dip is 1 in 8, and is fairly constant over the whole area, but the direction 

 varies within 35°. At Brighton the coal dips about 55°, at Fairfield 20°, 

 and at Abbotsford 32°, all south of east. The main seam averages 16 ft. 

 in thickness, reaching a maximum of 30 ft. near Christie's upper-mine 

 mouth. To the west of Christie's Creek the bed worked splits into two 

 seams, each with a thickness of 2 ft. 



The coal of the main seam may be classed as a good lignite, taking a 

 lignite as a coal that contains over 20 per cent, of water. Analyses of the 

 coal are given in the Dominion Laboratory Reports, 1907, p. 59, and Gordon 

 Macdonald's " Brown Coal of Otago," Colliery Guardian, 22nd November, 

 1912. 



The upper seams in places reach a thickness of 6 ft., but everywhere 

 are inferior to the main seam in quality. Very frequently pebbles of quartz 

 and bands of iron sulphide are met with in the coal. The iron sulphide 

 quickly oxidizes, and is probably chiefly marcasite. 



Quartz Sand. 



The quartz sand, which is well exposed in five quarries, has a thickness 

 of 50 ft., consists of loose well-rounded quartz-grains and rarely small frag- 

 ments of schist. The rock-fragments from which the sands were derived 

 must have suffered a great deal of attrition before only the quartz remained. 



In all exposures may be seen two textures of sand — fine and coarse — 

 generally showing current-bedding. Near the top is usually a band of 

 gravel or conglomerate, 1 ft. thick. Clay lenses occur in most of the 

 outcrops. 



The lower half of the sand at Gray's pit consists of coarse sand con- 

 taining pebbles ranging up to \ in. diameter. Above is 4 ft. 6 in. of fine 

 sand, succeeded by a cemented band of fine sand lin. thick and 1 in. of 

 clay. The clay is followed by 6 ft. of coarse sand, and then by fine sand 

 up to the band of conglomerate near the top. 



The pit owned by Freemans is rather spoilt by fireclay, which occupies 

 fissures that have been formed in the sand. Mr. E. R. Green informs the 

 writer that 5 chains to the north-west of this pit the fireclay was found 

 to have been intruded vertically through the coal-seams. A fissure had 

 been formed, the fireclay softened by Avater and squeezed up into the 

 opening by the pressure of the overlying rocks. 



