1891.] NEW YORK ACADEMY OF SCIENCES. 17 



III. T. S. Hunt, Feldspar from Chambly, 1. c, p. 98. 



IV. " Feldspar from ground-mass of Chambly dike after treatment 



with dilute nitric acid, 1. c, p. 98. 



V. and VI. H. Fiirstner, Zeitschr. f. Xtal., viii, 125, 202, 1883 ; Neues Jahrb., 



1884, ii, 171. 

 VII. J. H. Sears, On Keratophyre from Marblehead Neck, Bull. Mus. Comp. 

 Zool., xvi, No. 9, p. 170. 



In the further discussion of the basic dikes it will appear that in 

 the close association which they show in the field with bostonite we 

 have a mingling of rock types not unlike that long known at Mon- 

 treal,' ill many respects similar to that at Marblehead, near Boston,'' 

 and to the dikes recently brought to notice near Rio Janeiro, 

 Brazil.^ In all three localities they are associated with elaeolite- 

 syenite. This latter rock has not yet been discovered nearer to 

 Lake Charaplain than Montreal, which is one hundred miles north 

 of Burlington. It is not improbable that elaeolite-syenite may yet 

 appear in the eastern Adirondacks. 



The Breccia Bostonites. 



On the east side of Shelburne Point, which is just south of Bur- 

 lington, and also on the west side, a broad dike (20 feet) outcrops. 

 It is undoubtedly continuous between. It is a most remarkable 

 rock, and consists of angular pieces of slate and red quartzite ce- 

 mented together by an igneous base. The cementing base is not 

 very fresh in the attainable specimens, but is clearly of the same 

 nature as the ground-mass of the bostonites. The included frag- 

 ments are angular and seldom show any absorption into the igneous 

 rock. Two explanations may be advanced for this dike. One, that 

 it has been intruded on a line of previous faulting and attrition, 

 which have broken up the walls and have left loose material to be 

 gathered up by the rising magma. This explanation has the greater 



1 T. S. Hunt, papers cited nnder analyses I-IV above ; also, Geol. of 

 Canada, 1863, p. 655. B. J. Harrington, idem, 1877-78, p. 429. A. Lacroix, 

 Sur la Syenite-elaeolithique de Montreal, etc., Comptes Rendus, .June 2, 1890, 

 p. 1152, and Descriptions des Syenites nepehliniques de Pouzac, Hautes-Pyre- 

 n^es et de Montreal, etc.. Bull. Soc. Geol. France, 3, xiii, 1890, 511-558. 



2 A. Hyatt, Remarks on the Porphyries of Marblehead, Mass., Proc. Boston 

 Soc. Nat. Hist., xviii, p. 220, 1876. T. T. Bouv6, The Origin of Porphyry, 

 idem, xviii, p. 217. M. E. Wadswortb, The Trachyte of Marblehead Neck, 

 idem, xxi, p. 288 ; Geology of Marblehead, idem, xxi, p. 306 ; Zircon Syenite 

 from Marblehead, idem, xxi, p. 406. W. 0. Crosby, Geology of Eastern Massa- 

 chusetts. J. S. Diller, The Felsites and their Associated Rocks North of Boston, 

 Bull. Mus. Comp. Zool., vii, 165. J. H. Sears, Keratophyr from Marblehead 

 Neck, idem, xvi, 167. 



* O. A. Derby, On Nepheline Rocks in Brazil, etc.. Quart. Journ. Geol. Soc, 

 London, 1887, p. 457. F. Fr. Graefi", Mineralogisch. Petrograph. Untersuchung 

 von Elaeolith-syeniten von der Serra de Tingua, etc., Neues Jahrbuch, 1888, 

 ii, p. 222. Hunter and Rosenbuscb, Ueber Monchiquit ein Camptonitisches 

 Ganggestein aus der Gefolgschaft der Elaeolith-Syenit. Tscb., Min. u. Petrog. 

 Mitt., xi, 1890, p. 44. 

 Vol. XL— 2 



