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remarkable convergence of type, whereby rocks of widely 

 different origin come to assume identity of character, 

 explains the difficulty which has been experienced up to 

 the present time in arriving at a satisfactory conclusion 

 concerning their genetic relations. 



(a) Some of these amphibolites result from the meta- 

 morphism and recrystallization of sediments. To this 

 class belong the feather-amphibolites above described, 

 which usually occur in thin bands alternating with crystal- 

 line limestone, and are evidently of like origin. They 

 represent siliceous or dolomitic laminae in the calcareous 

 deposit. In many cases the bands of crystalline limestone 

 become thinner and less abundant, and the composite 

 rock passes gradually over into a body of pure feather- 

 amphibolite. Whether the granular amphibolite, which 

 is also found alternating with bands of limestone very 

 frequently and over wide areas, is in some cases of similar 

 origin, it has not been possible up to the present time to 

 decide. 



(b) Certain granular amphibolites represent altered 

 igneous intrusions, for they are found in the form of dykes 

 cutting across the stratified white crystalline limestone 

 on the shores of Jack's lake in the township of Methuen. 

 The limestones here dip at a low angle to the south, and 

 are excellently exposed in low cliffs about the lake. The 

 typical granular amphibolite can be seen rising above the 

 surface of the water in the form of vertical dykes one to 

 two feet (*3 to -6 m.) wide which cut directly across the 

 stratification of the limestone. These can frequently be 

 seen to have been diverted along certain bedding-planes 

 and torn apart by movements in these planes, the limestone- 

 strata having experienced somewhat extensive movements 

 along their bedding-planes during their upheaval. The 

 dykes, after following the bedding-planes for a certain 

 distance, once more cut vertically across them and 

 so reach the surface. Such dykes when seen on limited 

 exposures 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 completely recrystallized rock, and differs 

 from any of the normal igneous rocks. Under the micro- 

 scope it is identical with an amphibolite described by Dr. 

 Teall, which was developed by the alteration of a diabase 



