164 The Irish Naturalist. 



in places in the Co. Clare, such lines are evidently perpen- 

 dicular to the true bedding, as thej^ are also in some of the 

 *'Pipe-Quartzytes" of Sutherland, Scotland. 



The origin of quartz-rock is far from proved. So much 

 the better, as it is a field for j^oung geologivSts to work at. But 

 I, as an old hand, would advise them to look before they leap. 

 In places such as Howth; Carrick mountain, Co. Wicklow; 

 Forth mountain, Co. Wexford, when casually examined, it 

 seems to be bedded with the associated rocks. But in other 

 places, such as the Bannon district, Co. Wexford, etc., it is 

 undoubtedly intrusive ; and nearly invariably it has these 

 bedding-like planes often perpendicular to the walls of the 

 intrude, but sometimes parallel, as is the case in the d^-kes of 

 blackish quartz-rock, the adjuncts of the granilytes on the 

 north-east flanks of mount Leinster, Co. Wicklow. 



Quartz -rock, as a rule, is water-bearing, while quartzyte 

 is not ; quartz-rock ma}^ occur as an independent rock, as 

 intrudes or d5^kes in sedimentary rocks, or in granytes, or 

 as adjuncts of granj'te veins ; but when there are extensive 

 tracts of quartzyte, quartz-rocks nearly invariabl}^ are found 

 associated with them. These, where they occur, var}^ the 

 otherwise monotonous tract, as along them and associated with 

 them are springs, and consequently spots and tracts of vege- 

 tation ; this subject, however, will be more particularly referred 

 to in the second part of this paper. 



As my convictions as to the origin and advent of quartz- 

 rock have long since been published, it is unnecessar}^ to re- 

 peat them.' 



Quartzyte is perhaps the greatest puzzle of geology. As 

 far as my experience goes, there are no general rules by which 

 to determine the geological age of any isolated tract ; and the 

 most experienced worker may be stumbling about for months, 

 or even years, before he discovers that all his conclusions 

 are incorrect. 



The mapping of quartzyte and quartz-rock in Ireland was 

 originally mixed up. Griffith, indeed, seems to have had an 

 idea that there was a difference between them, and also in the 

 ages of the different tracts of quartz3^te, as he has coloured and 

 lettered them differently; but as his map is necessarily only a 

 general one, nothing definite can be learned from it. W5dey, 

 on his field-maps of Howth, Wicklow, and Wexford, has 

 mapped quartzj^te as distinct from quartz-rock, but in De la 

 Beche and Oldham's published maps his classification is 

 ignored. 



Subsequently John Kelly insisted that these rocks were of 

 distinct origin, the quartz-rock being intrusive or protrusive 

 but he was laughed at, although his paper w^as published in 

 the Jottr7ial of the Dublin Geological Society (vol. v., 1853, 



1 (( 



Geolog}' of Ireland," pp. 14 and 196. 



