On the Norian or " Upper Laurentian" Formation. 193 



oo P oo, that is to say it cuts off the acute prismatic angle 

 as oo P go does in the case of diallage. In sections which 

 show an optic axis and only one set of cleavages to 

 which the small rods lie parallel, the cleavage is seen to 

 be parallel to the plane of the optic axis. 



In all sections which contain the mineral, we find many 

 grains which show only one good cleavage to which the 

 extinction is parallel. 



In general it is like the augite quite fresh, in a few sec- 

 tions it appears however changed into bastite, and in a few 

 others into a serpentine like mineral. It sometimes con- 

 tains the dark scales and rods so often found in hyper- 

 sthene, but very often these are entirely absent. It is in- 

 deed a remarkable fact that in these Canadian rocks, the 

 iron-magnesia minerals contain only a few of these inclus- 

 ions while the associated feldspar is filled with them. We 

 have here a state of affairs the exact opposite to that in 

 the gabbros and associated rocks of the Scotch Highlands 

 which have been described by Prof. Judd. 



Hornblende. — This mineral does not occur in the 

 anorthosite of Morin except in a few places near the con- 

 tact with the gneiss. Then we always find it in intimate 

 association with the pyroxenes in the form of irregularly 

 defined grains generally about the border of the granulated 

 masses of pyroxene. It occurs as a general rule only in 

 very small quantity. It is usually green in color but is 

 often brown. It shows the cleavages, the small extinction 

 angle and the characteristic pleochroism of the species. In 

 a hand specimen from the neighborhood of the contact on 

 Lake l'Achigan, the maximum extinction angle was found 

 to be 15° and the following pleochroism observed: 



a=greenish yellow, ft=yellowish green, £=green. 



The absorption was c > ft > IX- 



In another hand-specimen, quite close to the contact, 

 about six miles north of New Glasgow, a brown hornblende 

 was likewise found in small amount. The extinction angle 

 was 18° with the following pleochroism: 

 a = light brownish yellow, ft = deep brown, £=deep brown. 



