288 Canadian Record of Science. 



is especially distinct at the same contact a little further to 

 the north on the road between the villages of Chertsey and 

 Rawdon. The rock here shows in an exposure of considerable 

 size, a very fine foliated structure due to an alternation of 

 thin bands of pure plagioclase with others of pyroxene. The 

 pyroxene layers might better be denominated leaves, since 

 they are very thin and appear in cross sections often as 

 mere parallel lines. The latter, as well as the plagioclase 

 layers, frequently show in thin sections under the micro- 

 scope, grains or fragments of large individuals, with tails 

 of small broken granules, which extend in both directions 

 from them, producing the foliated structure. This pro- 

 gress of granulation can be seen with astonishing distinct- 

 ness ; for, as just mentioned, the large crystals can be 

 observed in the very act of breaking up. In doing so, 

 they often break along certain lines, in which the broken 

 material is arranged. It can furthermore be observed 

 quite frequently that these grains are the remnants of 

 very large fragments which were broken apart almost 

 exactly in the direction of the foliation. They are thus 

 often very narrow but of considerable length. It even 

 happens sometimes that such fragments are twelve times 

 as long as they are wide. ^ 



At the upper end of the arm, where it passes into the 

 main area, the foliation becomes much less distinct, and 

 the rock gradually assumes the finely brecciated, irregular 

 streaked structure whose character and origin have been 

 already referred to. When the main area is finally reached, 

 definite strike ceases, except in a few places quite near the 

 limits. 



A cataclastic structure which is similar in many 

 respects to that which we have described, and in which 

 the grains of plagioclase are twisted and broken, and 

 likewise exhibit the granulation on their periphery, is 

 found in some of the distinctly striped hand-specimens of 

 the theralite of Mount Royal as above mentioned. We 



