DISCUSSION OF ORIGIN OP ALKALINE ROCKS 785 



Discussion 



Prof. J. F. Kemp remarked that the occurrences of ores like galeuite as 

 noted In the paper tend to confirm our conviction that many of the deposits of 

 the ores have igneous sources. 



ORIGIN OF THE ALKALINE ROCKS 

 BY B. A. DALY 



Published as pages 87-118 of this volume. 



Discussion 



Prof. J. F. Kemp: Professor Daly's suggestion will be productive of much 

 fruitful meditation. Nevertheless, from having seen several areas of nephelite 

 syenite, I think we should be cautious in inferring the influence of the lime- 

 stones now visible on magmatic differentiation. The observed relations are 

 those of a later body of igneous rock cutting limestones and only exerting con- 

 tact metamorphism, whereas for magmatic differentiation we must have the 

 calcareous rocks in the depths adjacent to the internal reservoir. This would 

 mean Archean limestones in most cases, and would place the matter beyond 

 observation and in the realm of hypothesis. 



COMPLEX OP ALKALINE lONEOUS ROCKS AT OUTTINGSVILLE, VERMONT 

 BY J. W. EQQLESTON" 



(A'bstract) 



This is an oval area of alkaline igneous rocks, stocklike, with roughly con- 

 centric arrangement and intrusive into gneisses. Syenite, with nepheline-bear- 

 ing varieties, is the chief type. There is also much essexite. The mass is cut 

 by numerous dikes, including tinguaite and camptonite. In chemical char- 

 acter the rocks are closely related to those of southern Norway, described by 

 Brogger. 



Discussion 



Prof. J. E. Wolff : On the old geological map of Vermont a number of round 

 or oval areas were marked in red as "granite." Of three of these, one in Stam- 

 ford, Vermont, is a coarse granite of the rapakiwi variety ; another is Ascutney 

 Mountain, described by Daly as a complex of alkaline igneous rocks, and the 

 third, also such a complex, as that at Cuttingsville. 



Mr. J. A. Dresser: The Monteregian hills in southern Quebec are a series 

 comparable to the Cuttingsville area, so well described by Mr. Eggleston. In 

 these hills, which rise at intervals for 50 miles in an east and west line, there 

 is a large development of essexite, accompanied by nepheline or alkali syenites. 

 Their composition, as indicated by the relative amounts of essexite and syenite, 

 grows less basic towards the eastern end of the series, and the Cuttingsville 

 area seems to be still less basic than the easternmost of these. The central 

 syenite seems to correspond most closely with the nordmarkite of Shefford 



"Introduced by J. E. Wolff. 



