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C. A. SUSSMILCH. 



portion of orthoclase, which however, is still subordinate 

 to the albite. The same field name viz : quartz keratophyre 

 is suggested. 



No. 3 Floiu. — This rock both in the hand specimen and 

 under the microscope is so similar to the No. 2 Plow that 

 a separate description is unnecessary. It also is a quartz 

 keratophyre. No chemical analysis of this rock has been 

 made. 



(b) The Kuttung Lava Flows. — These form a thick series 

 ranging up to a maximum thickness of 1,500 feet. This 

 thickness undoubtedly represents many distinct lava flows, 

 but as they are all very uniform in character one general 

 description will serve for all. 



In the hand specimen the rock is typically light-coloured, 

 generally greyish-white to cream coloured, where the rock 

 is more decomposed, as for example in the railway cuttings 

 just north of the Avon River bridge, the colour may be 

 greenish or reddish-brown. Flow structure is in many 

 places strongly developed, and in places also a certain 

 amount of contemporaneous brecciation has taken place, 

 just as is the case in similar lava at Pokolbin. The presence 

 of phenocrysts is rare, and when they are present they 

 usually consist of felspar and are small and few in number. 



Under the microscope the rock is glassy to cryptocrystal- 

 line, flow structure is commonly present, as also is spheru- 

 litic structure; the spherulites are small and rarely visible 

 in the hand specimens. Occasional small crystals of plagio- 

 clase felspar are seen in most slides; these are usually too 

 much altered to admit of accurate determination by their 

 optical characters, but these characters, as far as they go 

 indicate a felspar close to albite. More rarely small 

 crystals of quartz and orthoclase are seen. All the pheno- 

 crysts are much corroded. No ferro-magnesian minerals 

 have been detected, but occasional small patches of chloritic 



