156 TRANSACTIONS iSqq-'oo 



maximum, south of the Cypress Hills (3,800 feet). Here the 

 enormous intrusive masses of the Three Buttes, produce a violent 

 disturbing effect, drawing the astronomical parallel to the south, 

 at an average rate of 14 feet to a mile, for a distance of about one 

 hundred miles. When we actually enter the tumultuous Rocky 

 Mountains, with all their varied conditions of compositions, of 

 faults and dykes, and our lack of hypsometric maps, we are un- 

 able to even make a plausible estimate in which direction the local 

 deflection is to bfe expected. Even the relative deflection between 

 adjacent stations remains unknown in most cases on account of 

 the great difficulty in connecting them geodetically. 



As a very remarkable example of the deflection of the plumb 

 line may be mentioned, the one on the arc of the meridian be- 

 tween Andrate and Mondivi,in northern Italy, where in a distance 

 of a little over seventy-seven miles, a difference of nearly forty- 

 one seconds was found, that is to say the difference in the distance 

 between those two terminal points determined by direct astron- 

 omic observation, and also linearly by triangulation was found to 

 be about four tenths of a mile. How much of this quantity is 

 attributable to each place for local deflection, and again how much 

 is due to relief or topography, and how much to the unequal 

 distribution of masses beneath the surface of the earth, is not 

 known. 



It is evident that observations at two places which are also 

 geodetically connected, can onl}^ give the relative deflection of 

 the plumb line. 



For the boundary between the I^ake of the Woods to the 

 summit of the Rocky Mountains, the Commissioners agreed that 

 the line joining any two adjacent monuments shall be an arc of 

 the parallel. This was to apply, too, in the case of restoring any 

 monument whose position was lost. This agreement differs from 

 that of the boundary commissioners, who had charge, some 17 

 years previously of denning the boundary from the Gulf of Georgia 

 to the summit of the Rocky Mountains. They agreed that the 

 connecting line between monuments shall be a straight or direct 

 line, i.e. an arc of a great circle. 



The international boundar}^ commission appointed to define 

 the boundary under the first article of the Treaty of June 15th, 

 1846, (the present southern boundary of British Columbia) was 



