16 



TRANSACTIONS OF THE 



[OCT. 19, 



in the slide, it is shown by the loss to have suffered some alteration. 

 No. 102, taken from the Vermont report, p. 585, is the cementing 

 magma of a breccia dike to be later described. No. 11 is abnormal 

 and is of the coarsely crystalline dike of Shelburne Point, referred 

 to above. 



Loss 



SiO^ 



AlA 



Fe,03 



CaO 



MgO 



K^O 



Na^O 



Sp. gr. 



No. 11 was kindly analyzed by Mr. W. M. Morrison, resident 

 graduate in chemistry at Cornell University. The amount of soda 

 in No. 66 is very suggestive. As no well-marked plagioclase 

 appears in the slide, which is of a very homogeneous rock, the infer- 

 ence is strong that some soda orthoclase (anorthoclase) is present 

 and that the dike is really allied to the keratophyrs and pantellerites. 

 Years ago (1853-56) T. Sterry Hunt separated a number of feldspar 

 crystals from related dikes in the region of Montreal, and, as shown 

 by the accompanying analyses (I-IV inclusive), they furnish close 

 parallels. V and VI are analyses by Forstner of the anorthoclase 

 of the trachytic rocks of the island of Pantellera, and their simi- 

 larity with the older analyses of Hunt is very striking. Analysis 

 YII, by T. M. Chatard, of the keratophyr described by J. H. Sears, 

 from Marblehead Neck, is wonderfully like the others. The kerato- 

 phyr described by W. S. Bayley, from Pigeon Pt., Minn., is much 

 higher in silica (A. J. S., iii, xxxvii, 54). 



100.79 99.99 100.12 98.95 100.14 100.65 100.64 



I. T. S. Hunt, Feldspar from Brome (Canada), Trachyte, A. J. S., ii, xxxviii, 



97; Geol. Canada, 1853-56. 

 II. " Feldspar from Sliefford, Canada, 1. c, p. 97. F. D. Adams has 



described a rock from Shefford as quartz-free porphyry, 

 Geol. Canada, 1880, '81, '82, p. 10a. 



