172 THE CANADIAN NATURALIST. [JuDC^ 



tial analysis of the insoluble residue showed it to be a feldspar 

 allied to those of the preceding trachytes : the quantities of potash 

 and soda were however nearly in the ratio of four to three. 



A large dyke of trachyte in the limestone 'quarries at the Mile 

 End, near Montreal, is remarkable for the amount of carbonates 

 which it contains. It is grayish-white, with dark grey spots, gran- 

 ular, sub-vitreous in lustre, and holds a few crystals of hornblende. 

 By ignition it loses 11.0 per cent, of its weight. In powder it 

 effervesces freely with nitric acid, disengaging carbonic acid, and 

 when heat is applied, red fumes from the peroxydation of the iron. 

 100 parts of the rock yielded in this way the soluble matters 

 given under xii A. The composition of the residue, from 

 which the soluble silica was not removed, is given under xil. 



IX. I. XI. xir. 



Silica, 63.25 62.90 58.50 61.62' 



Alumina, 22.12 23.10 24.90 21.00- 



Lime 56 .45 .45 2.69- 



Potash, 5.92 2.43 4.66 



Soda 6.29 8.69 5.35 



Volatile 93 1.40 2.10 2.37, 



99.07 98.97 97.69 



A second determination of the alkalies in a portion of the tra- 

 chyte IX, which had not previously been treated by acid, gave 

 potash 5.40 and soda 6.49. A second analysis of x gave potash 

 2.28, and soda 7-95. 



IX A. X A. XI A. B. XII A. 



Silica, 1.43 5.00 



Alumina 2.43 1.27 1.32 4.84 



Peroxyd of iron 2.40 2.84 1.47 2.51 2.65 



Lime 60 1.86 4.14 3.50 6.49 



Magnesia 1,34 1.35 1.70 



Potash, 40 .25 undet. undet. undet 



Soda 98 .21 " " " 



Red oxyd of manganese, 1.31 .87 



• • • 



Of the matters soluble in nitric acid in the last-described trachyte, 

 XII, the lime in the form of carbonate would equal not less than 

 11.60 per cent, the magnesia 3.58, and the iron 3.82 per cent of 

 carbonates, in which condition by far the greater part of these bases 

 are probably present. 



