ELIZABETHTOWN AND PORT HENRY QUADRANGLES 3 1 



crushed and sheared varieties is often prevented by the intermedi- 

 ate rims of garnet to which reference will' be made later. 



Just east of Elizabethtown village in Green hill and Raven hill 

 as well as to the north in the Ausable quadrangle, the anorthosite 

 has much reddish brown biotite instead of the exclusive pyroxenic 

 mineral. The feldspar is also often reddish or brownish and as 

 crushing is not pronounced the rock looks much more like a coarse 

 mica-syenite or nephelite-syenite than like anorthosite. Yet micro- 

 scopic investigation has invariably shown the feldspar to be plagio- 

 clase of the normal type. 



The anorthosites are believed to grow more basic toward the 

 borders. The pyroxenic component becomes more and more pro- 

 nounced and in the end instead of forming 5 to 15 per cent of the 

 rock, it may be 25 or over. In this respect the writer's observa- 

 tions are in accord with those already published by H. P. Gushing 

 for the northwestern areas. The rock then shades into a very 

 coarse gabbro, but the plagioclase is always the most prominent 

 member and in the field in order to maintain the distinction be- 

 tween the anorthosites and the basic gabbros these varieties have 

 been called pyroxenic anorthosites. The sole difference is the 

 increase in the bisilicates. 



Another mineral of almost universal occurrence in the anortho- 

 sites is garnet. Over much of the area it is rare to find the labra- 

 dorite in contact with the titaniferous magnetite or pyroxene. 

 Almost always there will be an intermediate rim of garnet which 

 surrounds the pyroxene or iron ore like a little crown of highly 

 lefracting pink grains. Even in the hand specimens the rock is a 

 very beautiful one but under the microscope where the garnets 

 stand out in relief the effect is even more impressive. The garnet 

 rims are not limited to the anorthosites but are found in the rocks 

 of the next type and also in the basic gabbros under which they 

 will be again referred to as the garnets are accompanied by other 

 minerals. The rims rarely appear in the syenites. 



Larger masses of deep red garnets are also sometimes met, 

 looking like knots in a board. They have probably recrystallized 

 from pyroxenic material once present in the anorthosite. 



Chemical composition. No special analyses of the typical anor- 

 thosite from this area have been prepared. The rock seems so 

 simple in its mineralogy as scarcely tO' require them. Such analy- 

 ses, however, as have been made of similar types either in neigh- 

 boring or remoter localities, even including Norway, are given 

 below, together with the percentage composition in actual minerals 



