240 C. CALLAWAT 01<( THE GRANITIC AKD 



types of granite in the main granite district, one with two felspars, 

 the other white like an elvan, and containing sphene. This latter 

 appears in the island of Arranmore. There is a totally different 

 granite further south, near Barnesmore, and that does not exercise 

 metamorphic action on the neighbouring rocks. In conclusion, he 

 inquired, What relation did the beds in Wexford bear to the Silu- 

 rian near Enniscorthy ? 



Mr. Teall said that the two portions of the paper struck him 

 very differently. The first portion evidently contained a very in- 

 teresting record of carefully observed facts, the second portion dealt 

 with the correlation of the schists of the district with those of other 

 localities, — the only evidence for such correlation being a certain 

 lithological resemblance. He was extremely sceptical about the 

 possibility of determining the chronological relations of such rocks in 

 this way, and believed that some of the characters relied upon were 

 merely structural and mineralogical peculiarities, dependent upon the 

 mechanical actions which determine regional metamorphism. The 

 eruptive origin of certain foliated rocks had been clearly established 

 by Darwin, Forbes, Kjerulf, Lehmann, and many other observers. 

 The development of micaceous minerals in connexion with regional 

 metamorphism was a common feature ; and he especially referred to 

 the gneissose flagstones and associated schists of the north-west of 

 Scotland. The mica in these schists appeared to be developed at 

 the expense of felspar. In some cases " eyes " of felspar remained, 

 while in the more perfect schists these were almost if not entirely 

 absent. A quartz-felspar grit, such as the Torridon Sandstone, if 

 subjected to regional metamorphism, might thus be readily con- 

 verted into a mica-schist, and he was strongly inclined to think 

 that some of the eastern schists had been made in this way. 

 The Lough-Foyle and Kilmacrenan series of the author were 

 evidently the result of regional metamorphism, and possibly many 

 original groups had been involved in the actron. 



Mr. Blanfoed mentioned that some interesting evidence had 

 recently been brought forward by Colonel M*^Mahon, showing that 

 certain Himalayan gneisses were intrusive. If the differences 

 between the Lough-Foyle rocks and the Pebidian of St. David's were 

 such that these two could not have been identified by mineral 

 characters unless connecting links had occurred in Wicklow and 

 Anglesey, was it not absurd to endeavour to identify either of them 

 with beds in I*^orth America? The determination of the age of 

 rocks in distant countries by mineral characters had formerly been 

 applied to sedimentary beds, then to igneous ; it had long been 

 abandoned in the former, and was gradually being given up in the 

 latter, and there was much reason for caution in applying the same 

 key to ancient altered formations, the succession in which was often 

 very obscure. 



Mr. Mare considered that, in order for the correlation to be 

 safe, the Pebidian must be traced across ; but vulcanicity continued 

 up to and throughout Cambrian times, so that Cambrian rocks, if 

 altered, would be undistinguishable from the Pebidian. 



