I 



II 



III 



63.40 



63.60 



63.43 



12.70 



14.20 



14.20 



4.23 



1.92 



1.54 



3.37 



6.84 



2.35 



7.50 



4.37 



5.51 



.13 



5.09 



2.19 



7.95 



4.13 



3.49 



.40 



.70 



1.65 







.87 



SERPENTINES AND DIABASES 511 



of a diabase. In the coarse and central parts of the mountain the min- 

 eral olivine appears. The rock has the mineral composition of diorite; 

 bnt the hornblende is secondary and the rock therefore becomes a gabbro- 

 diorite. The two rocks are apparently differentiation products of a 

 single volcanic output.* 



Analyses by Huntf show the composition of the altered gabbro-diorite 

 and diabase mass under the head of diorites to be as follows : 



I. Diorite Si0 2 . , 



Brompton lake A1 2 3 . 



Orford, range XVI, lot 2. . .FeO . . 



II. Diorite MgO . , 



Saint Francois de Beauce.CaO.. 

 III. Granodiorite, Butte county .K 2 . . 

 Lassen peak, California : 



Na 2 0. 

 H 2 0., 



99.68 100.85 99.80 



Owls head (2,465 feet) is situated on the west side of lake Memphre- 

 magog, 16 miles south of mount Orford, which stands at the northern 

 end of the same lake. The level of this lake is about 682 feet above 

 sealevel. 



The rock at the eastern base along the lake shore is a common basic 

 phase of the pre-Cambrian volcanics. On the west side the adjacent 

 rocks are sedimentary. Between these the mass of the mountain has 

 been intruded. It consists, as far as yet known, of extremely altered 

 diabase, which was first determined by Doctor Adams. Sugarloaf, the 

 name by which a continuation of the Owls head mass toward Orford is 

 generally known, has been also shown by Doctor Adams to be similar in 

 composition. J 



Besides Orford, Owls head, and Sugarloaf, there are several hills along 

 this line, presumably similar in character. These are Hogs back, be- 

 tween the two mountains last mentioned; Hawk and Bear mountains at 

 the south of Owls head, and Carbuncle and other hills at the north of 

 Orford. So far as known, these hills are similar to Orford and Owls 

 head in general structure as well as in the character of the rocks com- 

 posing them. Fifty miles to the northeastward from Orford, Big Ham 



* J. A. Dresser : American Geologist, January, 1901. 



t Report Geological Survey of Canada, 1853, al. 



X Report Geological Survey of Canada, 1880-1881-1882, part A, appendix. 



