266 C. A. SUSSMILCH AND T. W. E. DAVID. 



some of these igneous rocks being intrusive sills has not been 

 lost sight of, but the available evidence is all in favour of 

 contemporaneous lava flows, with the possible exception 

 of the hypersthene andesite glass, but nowhere has a good 

 junction of this rock with those above and below it been 

 seen, consequently no very definite opinion can be expressed. 



The Tuffs. — These in general are similar in composition 

 to the associated lava flows, for example the tuffs above 

 the Martin's Creek flow are andesitic in character, whereas 

 those associated with the dacites are of a more acidic 

 character. They are typically fine-grained but are in parts 

 fairly coarse-grained giving characteristic volcanic breccias. 

 No large fragments or ejected blocks have been noted in 

 the tuffs proper. 



The Conglomerates. — Interstratified with the lava flows 

 are a number of beds of conglomerate, some of which con- 

 tain very large pebbles. At Martin's Greek the one just 

 above the hypersthene-andesite glass and which outcrops 

 in the railway cutting where the Paterson-Hilldale road 

 crosses the railway line, is a notable example. This bed 

 is crowded with granite pebbles, 12 to 18 inches thick, all 

 well rounded and waterworn. These beds range from 100 

 to 300 feet in thickness and are very persistent. 



The Mount Johnstone Series. — Following on the Martin's 

 Creek beds there occurs a series of tuffs, tuffaceous sand- 

 stones, conglomerates and mudstones, about 2000 feet in 

 thickness, with a final lava flow at the top, viz., the Pater- 

 son rhyolite, This series is very largely volcanic in origin 

 and its separation from the Martin's Creek beds is only 

 one of convenience, differing mainly in the absence of actual 

 lava flows. The tuffs are acidic to sub-acidic in character. 

 Beds of conglomerate are frequent, and their aggregate 

 thickness must be considerable. An excellent section of 

 this series may be seen on the eastern side of Mount John- 



