103 



the boundary line between the Province of Quebec and the 

 State of New Hampshire. The first mentioned is the most 

 westerly of the Appalachian folds in this region, while the 

 second forms the Capelton hills and Stoke mountain, and 

 the hills of Weedon farther to the north. 



The ridges contain a considerable development of 

 ancient volcanic rocks, porphyry, and greenstones. These 

 are overlain by sediments, some of which are probably of 

 Pre-Cambrian age. 



Closely bordering the southeast side of the Sutton 

 ridge, is a series of basic intrusive rocks. These rocks 

 constitute the serpentine belt, and contain the deposits of 

 asbestos and chrome iron ore. They extend from the 

 Vermont boundary line, with little interruption, north- 

 easterly to the vicinity of Chaudiere river. Representa- 

 tives of this series of rocks appear at frequent intervals in 

 the eastern part of North America, from Georgia to New- 

 foundland. In Quebec, they consist of peridotite and ser- 

 pentine, pyroxenite, gabbro, diabase, porphyrite, horn- 

 blende granite, and aplite, all of which are regarded as 

 differentiates from a single magma. They form hills 1,500 

 feet (457 m.) in elevation, which in some parts cover 10 to 

 20 square miles in area. Other exposures are only a few 

 hundred feet in width. The maximum width of any of 

 these areas rarely exceeds 5 miles (8 km.) and is usually 

 less than 1 mile (1 -6 km.). In structure they are considered 

 to form batholiths, or laccoliths, and intrusive sheets or 

 sills. 



Asbestos occurs in serpentine of two varieties which 

 are thought to be of different ages. They may be con- 

 veniently called the Thetford and the Broughton types, 

 and the rocks associated with them, the Thetford and the 

 Broughton series, from townships in which they are well 

 shown. 



In the area to be described the rocks of the serpentine 

 belt cut no rocks later than Sillery (Upper Cambrian), 

 though they probably alter Ordovician strata. To the 

 south of this district, however, in the county of Brome, 

 they cut strata of Ordovician age. It is not yet proven 

 that the rocks of the series were all intruded at or nearly at 

 the same time. Two periods of intrusion have however 

 been thus far determined, and others may yet be found. 

 Hence the age of the series as a whole can only be deter- 

 mined approximately. 



