450 mocEEDiNGS OP THE GEOLOGICAL SOCIETY. [June 21, 



Discission. 



Mr. FoKBES stated that none of the facts of this commnnication 

 were new ; but he dissented altogether from the conclusions arrived 

 at by the author in regarding these rocks as originally of sedi- 

 mentary origin, and for the following reasons: — (1) That this dis- 

 trict had been studied in detail by Mr. Scott and Prof. Haughton, 

 who declare the rock to be undoubtedly intrusive, as it not only_, 

 sends out veins into the neighbouring strata, but also encloses frag- 

 ments of the rocks through which it has broken. (2) Because the 

 author starts from the idea that if such rocks are found to He con- 

 formably on beds of undoubted sedimentary origin, it is a proof of 

 their being themselves sedimentary or stratified, — a conclusion which 

 is totally unwarranted, since there are innumerable instances, not only 

 of beds of lava or other igneous rocks being conformable to fossili- 

 ferous strata, but of their also being found intercalated with such 

 beds even for considerable distances. (3) The strata, so far from 

 being proved by him to be of truly sedimentary origin, are of a most 

 questionable origin, since they are neither in themselves fossiliferous, 

 nor can they be correlated with any containing fossils as proofs of true 

 sedimentary deposition ; and the description of his section is sufficient 

 to show this ; for although it looks well on paper on a scale of 3 feet 

 to the mile, the author has so little confidence in it that he is not 

 even certain as to which is the top or bottom of the section on 

 which so much generalization is based. (4) That a parallel struc- 

 ture equally, if not better, developed than any occurring in the 

 gneiss of Donegal is common to many volcanic rocks, as in a speci- 

 men laid before the meeting, in which this parallel foliated structure 

 due to crystallization-layers is so well developed as to make it appear 

 exactly like a stratified rock, and even split along these lines ; and 

 this, although the product of volcanoes still active, is found for 

 great distances both overlying conformably and intercalated be- 

 tween beds of the Cretaceous and Oohte formations, 



Mr. Scott was unwilling to accept the section given by the author 

 as satisfactory, but stated that Mr. Green had, without knowing of 

 the existence of his papers on Donegal, confirmed many of his obser- 

 vations. He agreed with him as to the bedded appearance of the 

 granite, and to the masses lying in general conformably with the 

 lines of stratification of the country. The nearest spot at which 

 fossiliferous rocks occurred was separated from the beds described 

 by the whole width of the county of Tyrone, though some presumed 

 Eozoonal forms had been found at a less distance. He was not pre- 

 pared to believe in the original absolutely fused condition of granite, 

 nor in there being two distinct types of granite, one metamorphic 

 and the other purely igneous. 



