180 H. p. CUSHIX(4 AUUTE-iSYENlTE (^NKIbb XEAJl LOON LAKE 



same, and that appears like a bomewhat crushed intrusive rock. When 

 it is recalled that the whole region has suffered profound dynamic met- 

 amorphism, producing a common foliation in the rocks irrespective of 

 their origin ; when it is further borne in mind that in the eastern half 

 of the Adirondacks the rocks of the Grenville (crystalline Hmestonej 

 series sehlom occur in considerable belts, but rather in mere patches, 

 and these ])atches are often wholly surrounded by undoubted igneous 

 rocks, being found not infrequently inclosed in the anorthosites, and, 

 further, that in the majority, if not in all cases, the bedding of the one 

 and the foliation of the other are parallel, the seeming difficulty in the 

 interpretation diHa])pear& ; when, finally, the chemical nature of the 

 rock is taken into consideration the case for its igneous origin seems 

 made out. 



It is not certain from the section whether the clastic rocks are in place 

 and cut by large dikes of the intrusive, or wdiether they represent frag- 

 ments caught up by the molten flood. Many examples of the latter 

 might be cited from the eastern Adirondacks, and the great extent of 

 the syenite in the vicinit}^ of Loon lake with the scarcity of the Gren- 

 ville series makes it the probable explanation here. Professor Kemp 

 concurs in the view^ that these patches represen*t the remains of a once 

 extended formation completely broken up by the great intrusions. 



Microscopic Character ano IMtneral Con&tituexnts 



The thin-section from the hand specimen chosen as typical and used 

 for the chemical analysis shows the presence of the following minerals : 

 Zircon, apatite, magnetitCj garnet, hypersthene, augite, hornblende, oligo- 

 clase, microperthite, and quartz. Other slides from the vicinity of Loon 

 lake show in addition biotite, titanite, allanite, and pyrite. The rock is 

 essentially composed of microperthite, augite, and hypersthene, with 

 quartz always present in vax-ying and commonly slight amount. 



Zircon and apatite are very sparingly present, are the only constit- 

 uents with idiomorphic boundaries, and occur in the usual microscopic 

 crystals as the earliest crystallization from the magma. 



IMagnetite is only in slight amount in irregular grains. 



Allanite and titanite are found in only one of the slides and in only 

 minute quantity. The titanite is of deep orange-brown color, like that 

 in the pyroxene-granulites found associated with the magnetites of the 

 Adirondacks. But two small fragments of allanite occur, so that its 

 diagnosis is perhaps not beyond question, though the optical properties 

 agree wholly with those of that mineral. 



