BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



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



AUGITE-SYENITE CIKEIS>S NEAR LOON LAKE, NEW YORK 



BY H. P. CURHIXG 



{Read before the Society December 30, 1898) 



CONTENTS 



Page 



Introduction 177 



Megascopic character 178 



Section near Loon lalte and its interpretation 178 



Microscopic character and mineral constituents 180 



Structure of the rocks 182 



Chemical analyses ^ 182 



Table of analyses 182 



Discussion .,183 



Geologic age 185 



Adirondack syenite areas 186 



J^oon lake 180 



Salmon river 187 



Diana . . 187 



Mount Defiance 187 



Big Tupper lake . 188 



Relationship to the anorthosites 188 



Similar petrographic provinces .' . 189 



Canada north of Montreal 189 



Lake Superior 190 



Norway ' 190 



Sequence of eruptions in the Adirondacks 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 



XXYTT-BuT-T Gfot Sor. Am , Vot 10, 1<^08 (177) 



