306 THE CANADIAN NATURALIST. [Vol. VU. 



of alumina has been denied by some chemists, we find Fresenius 

 stating that * " carbonates of the alkalies throw down from solu- 

 tions of alumina basic carbonate of alumina." Watts in his Dic- 

 tionary of Chemistry writes carbonate of alumina with a query 

 after it, and Valentin, of the Royal College of Chemistry, says 

 that carbonate of soda, or carbonate of ammonia, precipitates 

 from solutions of alumina " basic carbonate of uncertain compo- 

 sition."f Langlois, Wallace, and Muspratt have all regarded the 

 precipitate formed by alkaline carbonates as consisting of hydrated 

 carbonate of alumina, but each of them has assigned to it a 

 different formula. H. Rose, on the other hand, states that the 

 precipitate formed by carbonate of ammonia is a compound of 

 trihydrate of alumina with carbonate of ammonia. J We cannot 

 then, I think, confidently assert that a carbonate into which 

 alumina enters is unknown to chemistry, but simply that it is 

 one of those points upon which " doctors differ." I refer to it 

 here, because it has a certain bearing upon the mineral which is 

 the subject of this paper. 



This mineral is a carbonate, the principal bases in which are 

 alumina, lime, and soda ; the carbonic acid being considerably in 

 excess of the amount required to form neutral carbonates with 

 the bases other than alumina. It occurs in the joints of a 

 trachytic dyke near the western end of McGill College, and 

 having been first collected by Principal Dawson, has, in honour 

 of him, been called Dawsonite. 



The rock constituting the dyke was examined by Dr. Hunt 

 some years ago ; but no special analysis of the Dawsonite was 

 made, as sufficient material could not then be obtained. As the 

 composition of the dyke is of interest in connection with that of 

 the material filling its joints, I give Dr.' Hunt's description and 

 analyses. He says § : " The rock is divided by joints into 

 irregular fragments, whose surfaces are often coated with thin 

 bladed crystals of an aluminous mineral, apparently zeolitic. 

 Small brilliant crystals of cubic iron pyrites, often highly modi- 

 fied, are disseminated through the mass. The rock has the 

 hardness of feldspar, and a specific gravity of from 2.617 to 



♦Man. Qual. Chem. Anal. ed. by S. W. Johnson, M.A., p. Ill, 

 New York, 1869. 



f Text Book of Practical Chemistry. London, 1871. p. 175. 

 I Watt's Diet, of Chem. vol. I, p. 779. 

 I Geology of Canada, 1863, pp. 659, 660, 



