Wilson — Glaciation of Orford and Sutton Mts., Quebec. 197 



thought to be more accurate than the majority of the earlier 

 observations. The method employed was as follows : An 

 observer is stationed with one or two barometers at a point 

 whose elevation is known from a railway profile. This 

 observer takes readings during the working day at half-hour 

 intervals and the data obtained are used to plot a time-pressure 

 curve. In the field, barometers which were compared with 

 the base barometers, both at the beginning and at the end of 

 the day, were employed. The time of observation and the 

 temperature were noted in each case when the field readings 

 were taken. In cases where more accurate results were 

 desired the field barometers were kept at the field stations for 

 several hours and were read at half-hour intervals simultane- 

 ously with the readings of the base barometers. The eleva- 

 tions were later determined by reducing the readings obtained, 

 corrections being applied for atmospheric temperatures. In 

 this way a series of sixteen pairs of observations were taken 

 and the six most closely accordant sets of readings were used 

 in finding the height of Mount Orford as given here. In a 

 series of over one thousand readings made by this method dur- 

 ing the past two years, the writer has obtained some very 

 satisfactory results where checks were afterwards obtained 

 from railway profiles to determine the probable accuracy of 

 the method employed. 



General Character of the Topography of the District. 



The eastern margin of the plain of the St. Lawrence is 

 formed by the edge of a belt of crystalline and igneous rocks, 

 the northward extension of the Green mountain range into 

 Canada. The general trend of the structural lines of this belt 

 of rocks is about 20 degrees to the east of north and we find 

 that the trends of the main ridges and valleys in the vicinity 

 of Orford and Sutton mountains are in conformity with the 

 trends of the structural lines. The Sutton ridge, of which 

 Sutton Mountain is the most important peak, consists of a "cen- 

 tral mass of gneiss flanked by quartzites and schists. It is the 

 western of the two ridges which occur in this locality. Orford 

 Mountain is the culminating peak of the Orford ridge, a topo- 

 graphic feature which extends into Canada from south of the 

 Vermont boundary and lies immediately to the east of the Sut- 

 ton ridge. 



The central core of the Orford ridge is a diabasic rock and 

 it is flanked by schists and serpentines. Between Orford 

 mountain and the International boundry several minor peaks 

 are developed on the ridge, occurring in the order named — 

 Hog's Back, Sugar Loaf, Owl's Head, and Bear Mountain, the 



