428 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



This trough is bounded on the N.W. side by a range of mode- 

 rately elevated granitic and syenitic hills, which rise up without tilt- 

 ing or much disturbing the limestone, and follow the river all the 

 way to Quebec ; and from below the limestone on the S.E. there 

 crops a hard quartzose conglomerate, succeeded by a formation of 

 pyritiferous clay-slate, with a cleavage cutting the layers of deposit 

 in a N.E. and S.W. direction, which is that of their general strike. 

 The bounding rocks on both sides of the trough present a surface 

 undulating into hill and dale, and those on the S.E. give rise to a 

 picturesque country, very much resembling some of the slate coun- 

 ties of Wales. The plains between them covering the trough con- 

 stitute the valley of the St. Lawrence, and may occupy a breadth 

 of forty miles, and the nature of the material of which they are 

 composed renders it impossible to conceive a region more fitted 

 for the purpo>=es of agriculture. 



Between Montreal and Lake St. Peter, the plains on the south 

 side of the river do not appear to attain the elevation they exhibit 

 on the N.W. Occasionally so low, close by the margin of the stream 

 on both sides, as to allow the formation of marshes, the banks in 

 general present a height of twenty to thirty feet above the level of 

 the water; but on the N.W. side, and ranging with the river, at a 

 distance varying from one to six miles from the water's edge, there 

 occurs a sudden upward step in the land of about 100 feet, forming 

 an elevated terrace between this point and the granitic country al- 

 ready mentioned, which rises up in another step, and though undu- 

 lating in the interior, has a general additional elevation of 200 to 

 300 feet. 



The terrace at the foot of the granitic step has a very even 

 surface over a great area, slightly modified in a few places by the 

 protrusion of the underlying limestone through the soft deposit of 

 which it is composed. It is chiefly, however, in the beds, of the 

 rivers which cross the plain in their course to the St. Lawrence that 

 the limestone strata are visible; and some of these tributaries, dash- 

 ing down the side of the granitic step, cut at once into the terrace 

 below, very nearly to the level of the main stream, and winding 

 through the deposit in question, show it to possess considerable 

 depth. When any tributary has excavated so deep a passage, the 

 banks are occasionally subject to landslips, sometimes of a very 

 serious character, and having visited the scene of one on the banks 

 of the Maskinonge, it appears to me worthy of particular notice. 



The waters of the Maskinonge take their rise in a chain of moun- 

 tains to the N.W., and passing through a series of small lakes, fall 

 into one about nine miles in circumference bearing the same name. 

 Issuing thence they flow through about twelve miles of country be- 

 fore they are precipitated in a beautiful cascade down the side of 

 the granitic step on to the plain at its foot. Making a deep section 

 into this, they wash bare the outcrop of some limestone strata, 

 which exhibit a gentle dip of 3° to 4° southward ; and from this 

 point to the mouth of the tributary at the head of Lake St. Peter, 

 there is very little fall, with the exception of a spot six miles below 



