2 55 FRA NK D. ADA MS 



igneous intrusion an area of .422 of a square mile. The mean of a 

 series of closely concordant aneroid readings, corrected by com- 

 parison with barometers at the observatory of 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 surrounding plain, or 875 feet 

 above sea-level, the plain here having an eleyation 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 south- 

 ern 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 approxi- 

 mately 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 larare blocks 

 which have fallen from the steep upper slopes and extend out 

 from the foot ; on the southern is a gently sloping, terraced plat- 

 form 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 age 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 

 Royal. On the plain about the mountain no rock exposures are 

 seen. A mantle of drift covers it, and numerous erratic blocks 

 and bowlders are scattered about. These are largely gneisses 

 from the Laurentian highlands, but some of them are plutonic 

 rocks from other hills of the Monteregian group. The plain 

 about Mount Johnson is, however, stated by Ells, who has exam- 

 ined this district, to be underlain "presumably" by rocks of the 

 Utica-Lorraine division of the Lower Silurian. 



On ascending the mountain the first rock which is exposed 

 above the drift mantle is a very fine-grained dark hornstone, uni- 



