Quartzytes and Quartz- Rocks. 165 



pp. 240 and 255). An amusing scene took place at the dis- 

 cussion. An eminent chemist stated : '* It is a well-known 

 fact to chemists that quartz cannot be melted," when old Kelly 

 stood up and said: '' I know a Chemist who can melt quartz." 

 I guess he was right. 



When working in the west of Co. Galway, I wanted to 

 map these rocks separately, but Jukes objected. Subsequently, 

 however, Jukes examined for himself, and in his one-inch map 

 of Dublin, Wicklow, and Wexford, the quartzyte and quartz- 

 rock are distinctly lettered and coloured. 



In spite of what had been previousl}^ learned, when I read a 

 paper showing that quartz-rock must be either intruded or 

 protruded, there was such opposition to its publication by 

 the Irish scientific societies, that I withdrew it, and published 

 it in the Proceedings of the Ma7ichester Geological Society. 

 Now we seem to have gone back to the *' Dark Ages " again, 

 as in the maps and memoir of north-west Ireland, recently 

 published, these rocks are higgledy-piggledy. 



Quartzyte may be either metamorphosed (sheared) quartz- 

 rock, or metamorphosed sedimentary silicious accumulations. 

 It does not, however, necessarily follow that all quartz-rock, or 

 sedimentary silicious rocks, when metamorphosed (sheared) 

 should be changed into quartzyte; because, if the constituents 

 are suitable, such changes may produce silicious micalyte, 

 gneiss, or even a granitoid rock. The quartz-rock of the Carrick 

 mountain-range, Co. Wicklow, when traced westward into the 

 metamorphic area, becomes a silicious-gneissoid or granitoid 

 rock, and although called quartz-rock on Wjdey's working 

 maps, on Jukes' published maps it appears as granyte. In 

 the Bennabeola range quartzytes, Co. Galway, there are dykes 

 of quartz-rock now represented by fine granj^toid rocks or gra- 

 nular felsytes, while in the same range some of the original 

 sandstones are now micalytes ; also, in Co. Donegal, there 

 were obliquely laminated sandstones, that now in places are 

 represented by obliquely laminated massive gneiss. 



These sandstones of Co. Donegal are ver>'- interesting and 

 instructive. They occur as a middle zone in the Upper 

 Terrane. To the south-westward they are very much altered. 

 In the neighbourhood of Knock3^brin (Letterkenny) they are 

 much sheared. Further eastward, from Rathmelton to Lough 

 Swilly, they are massive rocks that can be roughly tooled, 

 while if followed still further eastward across Inishowen, they 

 are found to be a kind, compact rock eminently suitable for 

 the finest tool-work. Numerous other localities could be 

 referred to, if necessary'-, but those given ought to illustrate 

 the changes that take place owing to metamorphism. 



A tract or a massive dyke of quartz-rocks that has been in- 

 vaded by upthrusting and shearing, and partl}^ changed into 

 quartzyte is most unsatisfactory to work out and explain, as 

 irregular bits and tracts have not been affected by the shearing 



