4 FRANK D. ADAMS 
2. By the alteration of basic dykes and similar igneous intrusions. 
3. By the alteration of limestone through the action of the intruding 
bathyliths of granite. 
First mode of origin.—Some of these amphibolites result from the 
metamorphism and recrystallization of sediments. To this class 
belong the “feather amphibolites’”’ above referred to, which usually 
occur in thin bands alternating with crystalline limestone and 
evidently of like origin. They represent siliceous, argillaceous, and 
dolomitic laminae in the original calcareous deposit. In many 
cases the bands of crystalline lmestone become thinner and less 
abundant and the composite rock gradually passes over into a body 
of pure ‘‘feather amphibolite.” This rock can, in certain parts of 
the area, be traced into a comparatively unaltered variety, so that its 
original character is definitely determinable. Whether the “ granular 
amphibolite,’ which is also found very frequently and over wide 
areas alternating with bands of limestone, is in some cases of similar 
origin, it has not been possible up to the present time to determine. 
Second mode of origin.—Certain granular amphibolites represent 
altered igneous intrusions, for they are found in the form of dykes 
cutting vertically across the stratified white crystalline limestone on 
the shores of Jack’s Lake in the township of Methuen. The lime- 
stones here dip at a low angle to the south and are excellently exposed 
in the form of low cliffs about the side of the lake. The typical granu- 
lar amphibolite can be seen rising above the surface of the water 
in the form of vertical dykes, cutting directly across the stratification 
of the limestone. These are one to two feet wide and can frequently 
be seen on reaching a certain bedding plane to have been bent over in 
the direction of the bedding which they follow, and to have been torn 
apart by movements in this plane, the limestone strata having, during 
their upheaval, experienced somewhat extensive movements along their 
bedding planes. The dykes, after having followed the bedding 
plane for a certain distance, once more cut vertically across the latter 
and so reach the surface. Such dykes when seen on limited exposure 
of the bedded surface of the limestone, especially in contorted districts, 
would usually present the appearance of interstratified masses of 
amphibolite. 
This amphibolite has the regular allotriomorphic structure of a 
