BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 10, pp. 177-192, PLS. 19-20 .APRIL 1, 1899 



AUGITE-SYENITE GNEISS NEAR LOON LAKE, NEW YORK 



BY H. P. GUSHING 



(Read before the Society December 30, 1898) 



CONTENTS 



Introduction 177 



Megascopic character 178 



Section near Loon lake and its interpretation 178 



Mici'oscopic character and mineral constituents 180 



Structure of the rocks . 182 



Chemical analyses 182 



Table of analyses 182 



Discussion 1 83 



Geologic age 185 



Adh'ondack syenite areas 186 



]jOon lake 186 



Salmon river 187 



Diana 1 87 



Mount Defiance 187 



Big Tupper lake 188 



Relationship to the anorthosites 188 



Similar petrographic provinces 189 



Canada north of Montreal 1 89 



Lake Superior 1 90 



Norway 190 



Sequence of eruptions in the i\dirondacks 190 



Summary 192 



Introduction 



Field-work in a portion of the Adirondack region during the past two 

 years has disclosed the rather widespread occurrence of rocks which 

 resemble some phases of the anorthosites, and were classed with them 

 until inspection of thin-sections showed their quite different nature. 

 Similar rocks 'prove to be of frequent occurrence in the district, and to 

 have an extent and importance not heretofore recognized. They also 

 possess considerable intrinsic interest, so that some preliminary notice 



XXVTI— BuF.T.. Geoi.. Sor. Am., Vur,. 10, 1S98 (177) 



