On Some Dykes Containing Huronite. 29 



Island boulder, a sample of winch was contained in the Holmes collec- 

 tion in the Peter Redpath Museum. In the course of this investigation 

 he discovered some very grave errors in Thomson's description. " The 

 hardness for example is about 5^ instead of 3 J as stated by Thomson. 

 Instead of being infusible it is distinctly fusible (F about 5) while it con- 

 tains alkalies the presence of which is entirely ignored by Thomson. "(1) 

 Dana, in an old edi'.ion (2) of his mineralogy mentions Huronite 



under Prehnite, evidently deeming it an allied mineral. In 1889,(3) 

 the same author mentions Huronite along with Weissite and Iherite as 

 a supposed altered form of Iolite (Cordierite). In the same edition (4) 

 he also says " Thomson's Huronite is an impure anorthite-like felspar 

 related to bytownite, according to T. S. Hunt (priv. contrib.), ex- 

 cluding the 4'i6 per cent of water the Si02 would be 47 percent, 

 of the remainder." Again, in the same edition, Dana states (5) 

 "Huronite, Thomson (Min., I., 384, 1836) considered an altered 

 mineral near fahlunite by T. S. Hunt, occurs in spherical masses in 

 hornblendic boulders in the vicinity of Lake Huron." In the last 

 edifion of Dana's Mineralogy (6) the author, Mr. E. S. Dana, places the 

 mineral under anorthite on the authority of Dr. Harrington's paper in 

 the Transactions of the Royal Society of Canada, but Dana is wrong 

 in referring the analysis made by Mr. N. N. Evans, to the Huronite of 

 the Drummond Island boulder, for in reality it belongs to the Huronite 

 found by Dr. Girdwood near Pogamasing. Michel-Levy and Lacroix(7) 

 include Huronite among the decomposition products of Iolite or Cor- 

 dierite. The failure to assign to Huronite its rightful mineralogical posi- 

 tion arose from the fact that it was impossible to ascertain its true 

 nature by chemical analysis. It remained for the microscope to dis- 

 close its composite nature and to show its relation to the more widely 

 known " Saussurite." 



(1) See Trans- Royal Sue. Canada, Section III, 1886, p. S2. 



(2) System of Mineralogy, 3rd edition, 1850, p. 313. 



(3) See System of Mineralogy, 1889, p. 301. 



(4) See Idem, page 34.) 



(5) See Idem, page 485. 



(6) System of MineraWy, 1892, p. 340. 



(7) Les Mineraux des Roches, 1S8S, p. 174. 



