GEOLOGY OF THE SCHROON LAKE QUADRANGLE 

 Table i Thin sections of anorthosite 



No. 20, three-fourths of a mile southeast of summit of Hoffman moun- 

 tain; no. 23, by the road i mile northeast of Boreas river; no. 24, by the 

 stream i mile east-southeast of summit of Ragged mountain; no. 10, i 

 mile southeast of summit of Oliver hill; no. n, i l / 2 miles a little west 

 of north of Irishtown; mo. 12, lake shore just north >of Grove Point; 

 nos. 13 and 14, one-half of a mile west-northwest of Bigsby hill; no. 15, 

 by road at Loch Muller; no. 16, one-third of a mile west of Loch Muller; 

 no. 17, one-half of a mile south-southeast of summit of Severance hill; 

 no. 18, top of Hayes mountain; no. 19, by the brook southwest of Smith 

 hill; no. 21, near western summit of Sand Pond mountain; no. 22, near 

 cross-roads at Boreas river; no. 37, southern brow of Cobble hill. 



No. 17 of table i exhibits very fine reaction rims as follows: 

 (i) magnetite with rims of garnet; (2) pyrite with rims of 'garnet; 

 and (3) magnetite with successive rims of hypersthene and garnet. 



Both the Marcy and Whiteface types of anorthosite are quite 

 certainly differentiation phases of the same cooling magma, the 

 latter representing a chilled border or marginal portion. The one 

 type grades into the other, and nowhere has one been found 

 definitely to intrude the other. 



Special descriptions of Whiteface anorthosite occurrences. In 

 the Boreas river area the Whiteface anorthosite is mostly rather 

 uniformly moderately gabbroid and foliated with scattering bluish 

 labradorites, but some local variations from this composition and 

 structure were observed. Near the cross-roads at Boreas river 

 (no. 22 of table i) a ledge is unusually rich in pyroxene and quartz. 



