GRANITES 515 



The granite from the quarries at Stanstead shows an incipient cata- 

 clastic structure in the microscopic section, and in the mass a somewhat 

 distinct foliation, known by the quarrymen as the "rift." This structure 

 is apparently due to dynamic metamorphism and shows the granites to 

 have shared in the folding of the Appalachian uplift, and consequently 

 to have been intruded before that movement had entirely ceased. As 

 dikes of adjacent granite masses cut Devonian (Lower Helderberg) 

 strata on the shore of lake Memphremagog, these intrusives are thought 

 to be of late Devonian age. 



The later Dikes 



A series of dikes of much later age than any of the rocks hitherto de- 

 scribed is widely distributed throughout the region. They are compar- 

 atively fresh in composition and little disturbed in position. Campton- 

 ite, diabase, and bostonite are the chief rock types represented among 

 them. 



A camptonite at Eichmond was found by the writer* to consist of 

 hornblende and plagioclase, with accessory magnetite and apatite. A 

 little leucoxene and small aggregates of chlorite, serpentine, and calcite 

 indicate that some degree of decomposition has already begun in the 

 rock. 



The hornblende is brown in color and shows the extinction angle, 

 Cf\t, was observed to be as high as 17 degrees. 



This dike, which is about three feet wide, cuts lower Trenton limestone, 

 which had been greatly folded and distorted prior to the injection of the 

 dike. One or two other smaller dikes occur in the vicinity, and a small 

 hill near by is thought to be underlain by some igneous rock. 



In the vicinity of Sherbrooke, 25 miles south of this locality, dikes are 

 known to occur in several localities. 



Near the line of the Canadian Pacific railway, in the northern out- 

 skirts of the village of Lennoxville, there is a camptonite dike very sim- 

 ilar to the above. It cuts both pre-Cambrian volcanics and Trenton 

 slates. 



At the Howard mine, Ascot, a dike of olivine-diabase cuts pre-Cambrian 

 eruptions. 



In a paper entitled "Camptonites and other intrusives about lake 

 Memphremagog," : t Mr V. F. Marsters discusses a large number of dikes 

 in the Lake Memphremagog basin, distinguishing the granites, etcetera, 



* J. A. Dresser : A hornblende lamprophyre dyke at Richmond, Province of Quebec. 

 Canadian Record of Science, Montreal, January, 1901. 

 t American Geology, July, 1895. 



