BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 11, PP. 389-416, PL. 24 JUNE 13, 1900 



IGNEOUS COMPLEX OF MAGNET COVE, ARKANSAS 



BY HENRY S. WASHINGTON 



(Presented before the Society December SO, 1899) 

 CONTENTS 



Page 



Part I. — Geologic structure of the complex 390 



Introductory 390 



Geologic position 391 



Structure of the mass 39 1 



Obstacles to observation 391 



Williams' views 392 



Form of the area 392 



Eelation to surrounding shales 393 



The " Ridge " 394 



Arrangement of the igneous rocks. 394 



Transition forms 395 



Resume of evidence 396 



Alternative hypotheses 396 



Part II.— Petrology of Magnet Cove 398 



Description of the main igneous types 398 



General mineralogical features 401 



General chemical features 402 



Chemical relations 402 



Serial character 403 



The dikes 403 



General trend of the dikes 403 



The dike rocks 405 



Chemical composition 405 



The zonal arrangement 407 



Peculiarity of order of rocks 407 



Other instances 408 



Cause of differentiation 408 



General discussion of causes 408 



Different types of laccoliths 410 



Comparison with other regions 414 



Differentiation along two lines 415 



Summary 415 



LVI— Bunt. Geol. Soc. Am., Vor,. 11, 1899 (389) 



