208 On the Geology of the Island of Montreal. 



tions now under consideration, may be understood from the 

 following observations. 



Horizontal shell limestone, floors, as has been already stat- 

 ed, the plain surrounding the hill ; and without the least de- 

 rangement* invests its trap masses, to a variable distance, 

 from the summit of from one hundred and fifty to three hun- 

 dred and fifty feet, the lowest of these elevations being on the 

 north, and the highest on the south flank of the east division. 



From the hill, as from a centre, there pass in all directions 

 into the limestone, with a remarkably straight, unchanging 

 course, a great number of dykes, arms, or veins, of the com- 

 position stated above ; and perpendicularly, or nearly so. 

 They have been traced northeastwardly, for a mile and a 

 half. Those at Lachine may originate in the trap contiguous 

 to them. In the race-course, which is a level piece of ground, 

 full of old and new quarries of limestone, no less than fourteen 

 of these veins have been counted. They are best seen about 

 the middle, and near the hill, from whence they advance just 

 above the grass, like the base of long, ruined, walls. The 

 most common direction on the race-course is east ; the devia- 

 tions being usually trifling. They dip north at a very high 

 angle. At the northeast corner of the course, two veins cross, 

 but the place of intersection is hid by soil. A little to the 

 south of the stand a vein runs north north east. In the quarry 

 north of the course, two contiguous dykesf also run north 

 north east, that direction leading to the hill. The same is 

 the case with another vein, in a pine wood, two thirds of a 

 mile north of the course ; and a second vein, close at hand in 

 she same wood, passes north by east. Of three in Williams's 

 limestone quarry, (about one and a half mile north east of the 

 hill) that at the back of the house runs north, and another in 



* Except near a deserted house on the west road to St. Catharine, 

 where it is turned up edgeways in places : but perhaps not by the trap. 

 f The composition of one of these dykes has been given. 



