690 FRANK D. ADAMS 



Each of these methods of graphic representation has its pecuHar 

 merits, and each has also its disadvantages, which become mani- 

 fest when it is desired by means of them to compare a long series 

 of analyses, as for instance those representing a whole petro- 

 graphic province. 



In connection with some studies on the character and relations 

 of the very striking series of alkaline rocks composing the petro- 

 graphical province of the Monteregian Hills, which are now being 

 carried on at McGill University, the attempt has been made to 

 secure a more satisfactory expression of the chemical relations 

 of the rocks of this province by employing a graphic representa- 

 tion in three dimensions. It is desired in the present brief paper 

 to give an outline of the method employed and the result obtained. 



Each of the analyses, 36 in number, was first plotted in the 

 form of a curve which showed the actual and relative proportions 

 of each of the chief constituents present in the rock. These are: 

 silica, titanic acid, alumina, ferric oxide, ferrous oxide, lime, mag- 

 nesia, potash, soda, water, carbonic dioxide. 



The manganous oxide present was placed with the ferrous 

 oxide and any small percentages of baryta or strontia with the 

 Hme. For purposes of simplicity other constituents, such as 

 chlorine and sulphuric acid, which are occasionally present in 

 small amount, were neglected, although of course it would be 

 possible to represent them in the curve were it considered desirable 

 to do so. 



This curve was constructed by drawing a horizontal line, and 

 marking off on it a series of points at equal distances from one 

 another. At each of these points an ordinate was erected. On 

 the first of the ordinates was plotted the molecular proportion of 

 silica present in the rock. On the next ordinate the amount of 

 titanic acid was similarly plotted, and on each of the others in 

 succession the molecular proportions of the other constituents of 

 the rock in the order enumerated above was shown. The points 

 so obtained were then connected, and a curve thus constructed 

 which shows in graphic form the chemical composition of the rock. 

 In Fig. I there is seen the curve thus obtained for a camptonite 

 occurring in the form of a dyke cutting the Trenton limestone at 



