REPORT OF THE DIRECTOR I917 121 



A striking contact of the syenite with the Grenville gneiss is shown 

 by an exposure in the village of Saranac Lake to the east of the road 

 running north on the west side of the river. Here the syenite was 

 injected along the bedding planes of the gneiss by the process known 

 as " lit-par-lit " injection, producing a banded rock composed of 

 alternate layers of the two rocks. 



Apparently there are no exposures of the limestones of the Gren- 

 ville series present near Lake Clear, but perhaps remnants will be 

 found among the hills on more careful search. If such are encoun- 

 tered, contact effects will probably be shown. 



Inclusions in Igneous Rocks 1 



As has been pointed out, the great igneous intrusive masses prob- 

 ably engulfed the overlying rocks to an enormous extent, often 

 dislodging fragments which were melted, in whole or in part, and 

 absorbed by the molten mass. 2 Each of the different intrusives 

 probably floated off pieces of the preceding rocks, for we often find 

 blocks embedded in the anorthosite, syenite and gabbros. Fre- 

 quently the edges of these included fragments present a corroded 

 appearance showing that partial melting or solution has taken 

 place. 



The usual rocks thus found included in the prevailing formation 

 are members of. the Grenville series. They are numerous in the 

 east-central portion of the Adirondacks, but about Lake Clear they 

 are not so plentiful. The Mountain pond exposure, above referred 

 to, shows in a very clear manner inclusions of the anorthosite and 

 Grenville in the syenite. On the map it will be noted that a long 

 ridge runs northeast-southwest on the eastern side of Mountain 

 pond. The exposure is on the first knob of the ridge to the south 

 of the road which runs on the south side of the pond. The stone 

 quarry beside the road is of extreme interest, and will be referred 

 to again in connection with the diabase dikes. In many places in 

 the great anorthosite core the rock is singularly rusty in appearance 

 and is difficult of interpretation except by assuming that it has 

 melted and included sufficient quantities of the Grenville rocks to 

 show a marked change in composition. Grenville inclusions are 

 limited, as far as the writer's experience has shown, to the schists and 



1 For a fuller discussion of " Magmatic Assimilation," see R. A. Daly, " Igneous 

 Rocks and Their Origin," ch. 11. 



2 William J. Miller, " Magmatic Differentiation and Assimilation in the Adiron- 

 dack Region," Bui. Geol. Soc. Amer., 25:243-64. 



