SYENITE-SOAKED ANORTIIOSITE 483 



resembles syenite more than anorthosite, and in thin-section the half of 

 the feldspar that shows structures is about equally divided between 

 microperthite and plagioclase (oligoclase to andesine). Chemically also 

 the rock is an intermediate one, as will shortly be shown. The rock is 

 regarded as an anorthosite gabbro which has been penetrated and broken 

 up by syenite which has forced its way between all the granules of the 

 original rock, in precisely the same way that the Laurentian granite- 

 gneisses of the region have invaded and soaked the older amphibolites, 

 separating every grain from its neighbor and inclosing it with a film of 

 granite. Such granite-soaked amphibolites pass over by imperceptible 

 stages into gray gneisses, intermediate rocks which seem to have resulted 

 from the complete assimilation of the one rock by the other. In like 

 manner this soaked anorthosite gabbro is regarded as representing the 

 preliminary stage in the process which, when carried to completion, has 

 produced the basic border of the syenite by its complete digestion of 

 material from the gabbro. 



The Anorthosite Outlier in Litchfield Park 



Inspection of the map will show this outlier a half mile northeast of 

 Jenkins pond, near the western edge of the map. It is entirely in- 

 closed by syenite. The ordinary syenite of the vicinity is of the gran- 

 itic type, but as the anorthosite is approached this grades into the basic 

 type, which forms a zone around the anorthosite and sends dikes into it, 

 the numerous exposures on the hill summit showing the relations clearly. 

 We have here, then, a large inclosure of anorthosite in granitic syenite, 

 which latter rock passes into basic syenite as the anorthosite is neared. 

 It is not the most basic type of the rock, but distinctly more so than the 

 normal. 



Relations oe the Syenite to the Grenvillb 



There is no doubt that the syenite is a much younger rock than the 

 Grenville sediments, but there is much doubt as to the structural relations 

 which obtain between it and the Grenville belt which runs south from 

 FoUensby pond and which cleaves the syenite instead of bordering it. 

 No inclusions of undoubted Grenville rocks have been seen in the syenite, 

 nor does the syenite vary in character as the Grenville is neared, except 

 that the acid syenite changes back to the normal variety. Within the 

 Grenville area are occasional small knobs of syenite, which likely repre- 

 sent little offshoots from the main mass which cut the sediments, though 

 lack of contacts prevents any certainty in the matter. There is much in 



