216 Canadian Record of Science. 



plug itself has at the base, immediately above the horn- 

 stone collar, a somewhat elliptical outline, and measures 

 3,500 feet by 2,500 feet, the longer axis having a direction 

 N. 20° E. This gives the igneous intrusion an area of 

 .423 of a square mile. The mean of a series of closely 

 concordant aneroid readings, corrected by comparison with 

 barometers at the observatory at McGill University at 

 Montreal, shows that the highest point of the mountain 

 is 685 feet above the main street in the village of St. 

 Gregoire opposite the church, that is, above the surround- 

 ing plain, or 875 feet above sea level, the plain here 

 having an elevation above sea-level of 190 feet. It has a 

 somewhat dome-like outline, and forms a very striking 

 feature in the landscape. The slope on the southern side 

 is steep, in places precipitous, while to the north it is 

 more gentle. The accompanying photograph (Fig. 3), 

 taken from the railway station near St. Gregoire, which is 

 about a mile and a quarter distant from the mountain in 

 a direction approximately southwest, shows this profile, as 

 well as the little notch near the summit, caused by a 

 ravine which passes down the side. 



At the foot of the mountain, more especially on its 

 southern, southeastern, and southwestern sides, are 

 numbers of large blocks which have fallen from the steep 

 upper slopes and extended out from the foot ; on the 

 southern is a gentle sloping, terraced platform of drift 

 which in part buries these great blocks, forming a " tail " 

 probably due to the drift accumulating here on the lee 

 side of the mountain during the ice movements in the 

 glacial age. This drift, however, has been in part at least 

 reassorted by wave-action during the period of depression 

 which in this region followed the glacial ag« and during 

 which the sea covered the plain to a depth of several 

 hundred feet at least, as shown by the high level terraces 

 with shell banks on the slopes of Mount Koyal. On the 

 plain about the mountain no rock exposures are seen. A 

 mantle of drift covers it, and numerous erratic blocks and 



