Plate 



^ Vw, Uipp^l^^ -yy. J. Miller, photo 

 Photomicrographs of thin sections of gabbro from the stock on the south 

 side of Loon lake. Each magnified 15 diameters. 



In the upper figure the large central mineral is olivine completely sur- 

 rounded by successive rims of hypersthene. biotite (narrow and dark), and 

 garnet. Surrounding all are broad laths of labradorite. 



In the lower figure the large, black, central mineral is ilmenite. followed 

 by successive rims of biotite, hornblende, garnet and biotite. The second 

 and third — biotite and hornblende — rims are not separable in the photo- 

 i^raph. Surrounding all are labradorite crystals. 



