260 Transactions. 



Previous Petrographic Descriptions. 



In 1870 Sir James Hector (1) passed through the Waihi district. Ap- 

 parently he considered the andesitic rocks of the neighbourhood to be of 

 doleritic and basaltic character. On the Waihi Plains he noted the presence 

 of " trachyte " [? wilsonite]. To the eastward Hector observed hills capped 

 by " true rhyolite " or " quartzose trachyte " [spherulitic rhyolite with 

 quartz phenocrysts], and on the coast-line cliffs of " true trachyte agglome- 

 rate." 



In 1882 Mr. S. H. Cox (2), now Professor of Mining in the Royal College 

 of Science and Technology, London, made a flying survey of the Ohinemuri 

 Goldfield. Cox mapped the rocks near Waihi as " tufaceous sandstone" 

 [propylitic facies of andesites and dacites], dioritic rock, anamesite (?), 

 and rhyolite. 



About 1883 the late Professor G. H. F. Ulrich determined by micro- 

 scopic study the andesitic nature of the gold-bearing rocks of the Thames 

 district. Ulrich's work, though known only through a communication 

 made to Professor F. W. Hutton (3, p. 19) may be regarded as the most 

 important contribution ever made to New Zealand petrography. Hence- 

 forward the auriferous rocks at Waihi and in other parts of the Hauraki 

 Goldfield if resembling those at Thames were regarded as altered or de- 

 composed andesites — an essentially correct conclusion. 



In 1897 Professor James Park, apparently on the strength of micro- 

 scopic examinations specially made by Ulrich (3, pp. 27, 28) referred to the 

 rocks of the Waihi auriferous series as propylite resulting from the altera- 

 tion of hypersthene-augite-andesite (3, pp. 26, 87). 



It ought to be remarked that the two rock-specimens determined by 

 Ulrich were probably both from the andesitic rocks overlying the auri- 

 ferous series, and hence Park's determination of the latter as altered 

 hypersthene-augite-andesite can hardly be regarded as authoritative. Ap- 

 parently this writer at that time regarded the Waihi andesites as all of one 

 type and of one geological age. 



Park described the other volcanic rocks at Waihi as rhyolites, of which 

 he mentioned there were at least two distinct flows. 



In the same year as the publication last cited an important report on the 

 geology of the Cape Colville Peninsula appeared from the pen of Mr. Alex- 

 ander McKay (4). On page 59 are a few sentences referring to the auri- 

 ferous rocks in the neighbourhood of Waihi. These are placed in the 

 " Kapanga group," but, evidently by design, no specific rock-names are 

 given. In the absence of proper microscopic determinations McKay's 

 attitude of reserve may be regarded as being highly correct. The various 

 rhyolites near Waihi are described (pp. 67, 68) as " spherulitic rhyolite," 

 " a remarkable brecciated rhyolite " (wilsonite), and " an earthy compact 

 rhyolite." 



Largely as a result of the boom in gold-mining that prevailed during the 

 years 1895-97, a number of papers in which the nature of the rocks at Waihi 

 was more or less cursorily mentioned made their appearance, but for the 

 purpose of the present article it is not necessary further to mention these 

 publications, which were nearly all of an ephemeral character. 



In 1899 the late Mr. F. Rutley, in association with Professor Park (5), 

 described several rhyolites from the neighbourhood of Waihi, as well as a 

 doubtful silicified rock, a supposed silicified andesite tuft", and a supposed 

 silicified andesite. Rutley M-as the first to observe tridymite in the rhyolites 



