498 J. A. DRESSER IGNEOUS ROCKS OF EASTERN QUEBEC 



imately square, and it was further subdivided into ranges and lots, ac- 

 cording to the English method, instead of being formed into seigniories 

 and parishes, after the old French mode of survey. 



Geography of the Kegion 



The general trend of the hills of the eastern townships is a northeast- 

 erly one, conforming to the direction of the Appalachian folding, the 

 successive ridges growing higher as they are more remote from the Saint 

 Lawrence valley. The principal rivers, such as the Yamaska, Saint 

 Francis, Mcolet, Becancour, and Chaudiere, cross these hills about at 

 right angles to their course and drain the region into the Saint Lawrence. 



The tributaries of these rivers take their direction from the Appa- 

 lachian folds and generally flow in either northeast or southwest courses. 

 The tributaries are therefore subsequent to the Appalachian hills, while 

 the main rivers are either antecedent to the later stages of that uplift or 

 have been superposed upon these older rocks by the extensive denudation 

 of the region; hence the tributaries are commonly much younger than 

 the main rivers. From these facts and also since the course of chief 

 glacial action has been parallel to the valleys of the principal rivers and 

 transverse to the tributaries, it results that many of the latter empty 

 into the former by falls and rapids. The water which these furnish has 

 given rise to several manufacturing centers, as the city of Sherbrooke, 

 where the Magog falls into the Saint Francis, and the town of Windsor 

 Mills, at the junction of the Wattopekak with the same river. The prin- 

 cipal rivers thus give cross-sections of the region, while the tributaries 

 usually afford much less information regarding the underlying rock. 



General Geology 



With the exception of a few small outliers of Devonian, the sedimentary 

 rocks of the Eastern townships are now considered to be pre-Silurian in 

 age. Silurian strata occur a short distance to the north of the district 

 in question and small outliers may be found within it, but thus far none 

 have been definitely determined. To the Cambro- Silurian have been 

 assigned certain of the limestones, the calcareous and ferruginous slates; 

 to the Cambrian, part of the quartzites, graywacke, and clay slates; 

 while similar rocks, with the exception of the clay slates, are referred to 

 pre- Cambrian, as well as the large areas of slate characterized by the 

 presence of chlorite and epidote. 



Igneous rocks are found to underlie the earliest sediments, to be inter- 

 calated among them, and to be intrusive through even the latest. 



