20 TRANSACTIONS OF THE [oCT. 19, 



almost nothinf^ of a dia.irnostic character. Clay or kaolin, calcite, 

 limonite, and indefinite dirt make up the slide. Very little recog- 

 nizable epidote has been noted. 



An interesting and exceptional alteration is afforded by the dike 

 at Palmer Hill, near Ausable Forks. The feldspar has yielded a 

 colorless, negative, uniaxial, rather brightly polarizing mineral with 

 abundant rectangular cleavages. This is scapolite. It often forms 

 secondary nests with quartz. Scapolite as an alteration product 

 from plagioclase has long been known in connection with various 

 rocks which are associated with the apatite deposits of Norwa}^, and 

 has more recently been discovered in the same relations in Canada.^ 

 The process has been discussed by Judd.'^ It is urged that solutions 

 of sodium cliloride penetrate the plagioclase along " solution 

 planes,"^ after which dynamic metamorphism in connection with the 

 sodium chloride changes the plagioclase to scapolite. In the present 

 instance there seems to have been no d3'namic metamorphism, but 

 it is likely that infiltrating sodium chloride or of hydrochloric acid 

 may have aided the change. Lacroix has also recently described 

 the alteration of plagioclase to dipyr, in a diabase of the Pyrenees.* 



The Palmer Hill dike yielded, on analj^sis, the results in column 

 I. By its side is placed for comparison No. II, which is the 

 analysis of a diabase from near Boston, and No. Ill is one from 

 the Keene Valley. 



I. 



SiOj 



Al,03 



Fe,03 



FeO 



CaO 



MgO 



MiiO 



KjO 



Na.,0 



Ti(l 



P,0 



COj 



FeS^ 



Loss 



TiO, 

 P,0. 



Sp. gr. 



' F. D. Adams and A. C. Lawson, On some Canadian Rocks containing 

 Scapolite, etc., Canadian Record of Science, 1888, p. 185. The paper gives 

 copious references to the literature and a valuable review of the same. 



2 J. W. Judd, on the Processes by which a Plagioclase Feldspar is converted 

 into Scapolite, Mineralogical Magazine, vol. viii, p. 186. 



3 For the description of solution planes, see J. W. Judd, Q. J. G. S. xli, 

 383, 1885 ; xlii, p. 82, 1886 ; Mineralog. Mag. vii, p. 81, 1886. 



* A. Lacroix, Sur les Phenomenes de Contact de la Syenite elaeolithique de 

 Pouzac, Comptes Rendus, No. 110, p. 1011, 1890, 



5 W. H. Hobbs, On the Petrographical Characters of a Dike of Diabase in 

 the Boston Basin, Bull. Mus. Conip. ZoiJl., xvi, 1. 



6 A. R. Leeds, Notes on the Lithology of the Adirondacks, 30th Ann. Rep. 

 N. Y. State Museum, p. 102. 



