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The Ottawa Naturalist. 



Vol. IX. OTTAWA, MAY, 1895. No. 



ON SOME DYKES CONTAINING " HURONITE." 



By Alfred E. Barlow, M.A. 

 Geological Survey Department, Ottawa, Canada. 



( Read be fore the Geological Society of America, Baltimore, Dec. 28th, iSg4- ) 

 The name Huronite was long ago given by Dr. Thomson of 

 Glasgow, to certain light-yellowish green masses or crystals which 

 occurred porphyritically embedded in a boulder of diabase found on the 

 shores of Drummond Island, Lake Huron, specimens of which had 

 been sent to him by the late Dr. Holmes of Montreal. Thomson 

 regarded it as a new species and published a description and analysis of 

 it in his Mineralogy of 1836. The occurrence of these crystals was 

 first noticed by Dr. Bigsby in 1820, who writes of the rock containing 

 them in a general way as "greenstone porphyries having a light-colored 

 base and containing crystals of red or white felspar seldom of both in 

 the same block,"(i) This brief and general description would not have 

 been sufficient for purposes of identification except for the fact that his 

 manuscript report which formed the basis of this paper, (2) was lately pre- 

 sented to the library of the Geological Survey of Canada. In the appendix 

 Dr. Bigsby notes " among the debris of the shore of Lake Huron are por- 

 phyries of greenstone with embedded crystals of red felspar or of four 

 or six sided prisms of cream white colour, foliate fracture, cleavage about 

 6o, yielding to the knife readily, translucent at the edges and of a feel 

 slightly soapy. Their crystallization is seldom well defined, but some- 

 times remarkably so." This clear and accurate description serves at 



(1) Trans. Geol. Soc. London, Vol. 1, p. 205. On the Geography and Geology 

 of Lake Huron, read Feb. 21, March 7 and 21, 1823. 



(2) Notes on the Topography and Geological structure of the north-west portion 

 of Lake Huron, addresseed officially to Dr. J. Wright, Inspector of Hospitals in 

 Canada and dated Quebec, Feb. 23, 1821. 



"(Commit icated by permission of the Director ) 



