Dresser — Geology of Brome Mountain. 



357 



areas occupied by the three rock types at Brome were ascer- 

 tained by placing a tracing of the map upon a sheet of square 

 ruled paper and counting the squares occupied by each. 



Taking the area of laurdalose as the unit, nordmarkose 

 and the hessose occupy 150 and 110 units respectively. Multi- 

 plying their analyses by these coefficients of area, and divid- 

 ing the sum of the products by the sum of the coefficients, the 

 mean of the means obtained is that given as analysis XVII. 



The analyses of the three related rocks in Shefford Mountain 

 were treated in a similar manner, and the result given as analysis 

 XIII. 



But since the two mountains are to be regarded as parts of 

 the same laccolite it is necessary to find the average of these 

 means. This having due regard for the area of the two masses 

 is found to be that given under XVIII. 





XVII. 



XIII. 



XVIII 



Si0 2 



._ 54 25 



59-51 



55-47 



TiO, .... 



1-23 



•78 



1-13 



Al.O,.... 



22-14 



1790 



21-17 



Fe.O..... 



.. 2*03 



2-17 

 2-64 



2-07 



■*■ ^2 3 



FeO 



2-66 



2-66 



MnO ._.. 



-12 



•45 



•20 



MgO .... 



1-48 



1-27 



1-44 



CaO 



6-77 



3-09 



5-93 



K 2 



__ 3-23 



4-46 



3-52 



NaO 



4-95 



5-98 



•27 



1-00 



5*19 



PO 



-17 



•12 



"""2 6 



HO 



-98 



•99 











100-01 



99-52 x 



99-89 





xBaO . 



-08 







C0 2 .___._ 



-13 







S0 3 



-]4 







CI 



-08 





A rock having the composition of the mean of Brome Moun 

 tain should be classed as follows in the Quantitative Classifica- 

 tion : 



Class I, Persalane 



Order 5, Canadare 



Rang 3, (alkalicalcic) 



Subrang 4, (dosodic) 



The mean composition of Shefford Mountain, XIII, would 

 be classed thus : 



Class II, Dosalane 

 Order 5, Germanare 

 Rang 3, Andase 

 Subrang 4, Andose 



