REPORT OF THE DIRECTOR I912 



97 



irregular mass of acid plagioclase or a crystal of biotite may lie 

 between the garnet arid the hornblende rim. As a rule the horn- 

 blende rims increase in width with the size of the garnets, some 

 rims being as much as two or three inches wide. These reddish- 

 brown garnets, completely surrounded by the black hornblende 

 rims which are, in turn, imbedded in the gray gneiss matrix, pre- 

 sent a striking appearance in the walls of the great mine pits. 



Geologic and topographic sketch map of portions of the North Creek 

 and Thirteenth Lake (U. S. G. S.) sheets, showing the mode of occurrence 

 of those garnet deposits which are lenslike inclusions in the syenite or 

 granite. 



This garnet-bearing rock clearly occurs as a long, narrow, lens- 

 like inclusion of Grenville gneiss in the great mass of Gore moun- 

 tain syenite. The inclusion is fully three-fourths of a mile long, 

 with nearly east-west strike. Several large openings have been 

 made in it and, in the very large more easterly pit, the width of 

 the inclusion is more than one hundred feet. The garnet rock is 

 removed by blasting and reduced by sledge hammers after which 

 the garnets are picked out by hand. 



2 In the Oven mountain mine the mode of occurrence is pre- 

 cisely like that in the Rogers mine. In thin section the matrix 



