26 The American Geoloijtst. July, 1895 
CONTENTS. 
Page. 
(Jeneral stratigraphy of the lake shore 26 
Tlie dikes 28 
Granite dikes 28 
Laniphrophyre dikes 29 
Microscopic description of tlie dikes 30 
Granite dikes 30 
Laniphrophyre dikes 31 
Diabase 31 
Camptonite 32 
Augite caniptonite 33 
Summary of literature on other occurrences of camptonite 35 
Monchiquite dikes 36 
Summary of literature on other occurrences of monchiquite 37 
Fourchite dikes 38 
Geneual Stratigkaphy of the Lake Shore. 
In the northeast corner of Vermont and extending across 
the line into the province of Quebec for several miles is one 
of the most picturesque bodies of water to be found in that 
region. This unique lake has long been known as lake Mem- 
phremagog. It is somewhat crescentic in shape, but has a 
general north antl south trend. The contour of the surround- 
ing country and the shape and position of the lake, as com- 
pared with others in the same region, suggest that the de- 
pression now occupied by this body of water was produced 
by glacial agents. It is evidently not due to a downward 
folding of the Paleozoic strata, for there is little or no evi- 
dence of such a movement. On the other hand, the prominent 
elevations, especially those on the west side of the lake, as 
well as the shores, with their occasionally eroded surfaces, all 
point to the conclusion that the depression was produced by 
glacial erosion. 
Along the southeastern shore there is sulticient accumula- 
tion of drift to render an examination of the country rock 
impossible. A few of the islands at the southern extremity 
of the lake are made up wholly of drift material, while those 
in the central parts consist of rounded domes of schistose and 
shaly rocks, having resisted to a remarkable degree the erod- 
ing effects of moving ice. 
A brief examination of the stratified rocks, as exposed 
along the shores toward the north, has led the writer to be- 
lieve that they represent the lower members of the Paleozoic. 
Starting from Magog, at the northern extremity of tiie lake, 
the rocks exposed on either side for some distance to the 
