Selwyn — Geological Age of the Saganaga Syenite. 



!19 



Fig. 3 shows the microscopic structure. The dominant 

 cleavage is evidently slip-cleavage, and the cleavage-foliation 

 itself shows in places extremely minute plications. 



Figs. 3, 4, from photographs of thin sections ; 3, section - 12 in. sq. ; 4. section 

 0'30 in. sq , the directions of the clip are here figured reversed. 



Fig. 4, under less enlargement, shows the flexure of the 

 cleavage-foliation which in this specimen is considerable. In 

 both figs. 3 and 4 the prominence of the cleavage-foliation is 

 due to the infiltration of ferruginous matter. 



The steps in the formation of this structure appear to have 

 been : 



1. Plication of the beds and consequent cleavage-foliation 

 (I), slip-cleavage. 



2. Plication of cleavage-foliation (I) in consequence of sec- 

 ondary pressure operating in the direction of the cleavage dip. 



3. Cleavage-foliation (II), slip-cleavage passing into close 

 joint cleavage, produced by the plication of cleavage-foliation I. 



This subject is not only of interest structurally but in some 

 regions may be of economic importance. 



Newport, R. I., Jan. 2, 1892. 



Art. XXXIX. — Geological Age of the Saganaga Syenite', 

 by A. K. C. Selwyn. 



I am surprised to read in a paper by H. V. Winchell* upon 

 the age of the Saganaga syenite the statement that this 

 Saganaga syenite was always supposed to be Laurentian. A 

 glance at the Canadian Geological map, 1882, shows it as occur- 

 ring with an extensive area of Huronian. That it should be 



* This Journal, vol. xli, May, 1891. 



