102 



These furnish the principal water-powers of the district, 

 and have given rise to such manufacturing centres as the 

 city of Sherbrooke, at the junction of the Magog with the 

 St. Francis; and Windsor Mills, at the entrance of the 

 Wattopekah to the same river. 



General Geology. — Southeastern Quebec is underlain 

 by strata of Palaeozoic age, resting upon the Pre-Cambrian 

 complex, which emerges from beneath the later rocks a 

 short distance north of the St. Lawrence. The Palaeozoic 

 strata form an ascending series toward the southeast, 

 except where folding and subsequent erosion have dis- 

 turbed the sequence. Every geological formation from 

 Cambrian to Devonian is represented. 



The structure is far from uniform. In the north- 

 western part of the St. Lawrence plain, the strata are 

 conformable from Potsdam to Hudson River. They are 

 little disturbed in position, and dip toward the southeast 

 at low angles, usually 5 to 6 degrees. This regularity ends 

 abruptly at the St. Lawrence and Champlain fault, a great 

 dislocation which extends from the foot of Lake Champlain 

 northeasterly to Quebec city, and runs thence to the Gulf 

 of St. Lawrence along or near the present channel of the 

 river. 



On the southeast side of this fault the strata are highly 

 folded, and have otherwise suffered greatly from regional 

 metamorphism. The conditions of deposition on this side 

 were also different. The marine fossil fauna indicate cold, 

 perhaps subarctic, conditions, and an unconformity is 

 found at or near the base of the Ordovician, which is not 

 found on the west side of the fault. 



Over considerable areas east of the fault, the folded 

 rocks have been planed down by erosion, so that they now 

 underlie the eastern part of the St. Lawrence plain without 

 expressing their structure in the topography. The sedi- 

 ments of the region consist of shales, limestones, and sand- 

 stones, with schists, slates and quartzites on the east side 

 of the great fault. 



The Highlands, or Notre Dame hills, consist of three 

 parallel, anticlinal ridges running in a northeasterly direc- 

 tion, with two broad, intervening basins, each of which 

 has a width of about 25 miles (40 km.). The ridges are 

 usually distinguished as the Sutton, Sherbrooke or Stoke, 

 and Lake Megantic anticlines. The last forms a part of 



