On the Norian or "Upper Laurentian" Formation. 289 



must here consider them' as the result of a movement 

 which took place before complete consolidation, and as an 

 example of what Brogger 1 designates as " protoclastic 

 structure." It is here, however, found only locally, and is 

 not noticeable in many sections of the rock. Yet its 

 occurrence is of interest for the reason that it proves that 

 its mere existence is not always an infallible sign that the 

 rock has been exposed to great pressure, and has been' 

 crushed. 



Although in the anorthosite this granulation, with its 

 accompanying phenomena, are without doubt caused by 

 the pressure to which the rock had been subjected, the 

 effects of this pressure are quite different from those 

 generally observed. 



In a foliated structure caused by shearing, as Lehmamm 

 and others have so excellently shown, in many instances 

 the breaking takes place along certain lines. Along these 

 lines or stripes, which sometimes are quite wide, and at 

 others quite microscopical in size, the rock is finely broken 

 up, so that it forms what Heim calls " Kutschmehl " in 

 cases where it has not again become thoroughly compacted. 

 Between these shearing planes we often find comparatively 

 few indications of pressure. Especially along the lines of 

 movement, and when these are absent, through the whole 

 rock, in places where extensive dynamic effects have 

 occurred, certain peculiar alterations in the constituents 

 of the rock are observed. 



Of these the following deserve special mention : — The 

 alteration of the pyroxene into hornblende and of the 

 plagioclase into a mixture of zoisite, albite, and other 

 minerals, which is known under the name of saussurite. As 

 far as could be ascertained no undoubted case has as yet 

 been observed among the crushed gabbros and associated 

 rocks where uralite and saussurite have not been found. 



i BioggHr, die Miueralien der Syenitpeginatitg&nge der sudnorwigischen Angit und 

 Hephelin— Syenite. Zeitsehr, fur Kr. Bd., 16, 1890, p. 105. 



