USE OF TERM "OPHITIC" 661 



On motion, the action of the Council was endorsed and the committee 

 given authority to act for the Society. 



The Society then divided into two sections, and the following papers 

 were presented under the chairmanship of President Calvin: 



CLASSIFICATION OF CRYSTALS BASED UPON SEVEN FUNDAMENTAL TYPES 



OF SYMMETRY 



BY CHARLES K. SWASTZ 



This paper has been published as pages 369-398 of this volume. 

 The paper was discussed by W. H. Hobbs, E. H. Kraus, W. N. Rice, 

 and H. B. Patton. 



The following paper was read by title : 



USE OF "OPHITIC" AND RELATED TERMS IN PETROGRAPHY* 

 BY ALEXANDER N. WINCH ELL 



Contents „ 



Page 



Introduction 661 



Present usage 662 



Original definition 662 



Usage of Michel Levy 663 



Related terms 664 



Summary 666 



Introduction 



For thirty years the term "ophitic" has been used in petrographic descrip- 

 tions to describe certain textures found in basic igneous rocks, especially dia- 

 bases. It is today used more or less currently wherever such rocks are studied 

 microscopically. And it may be perhaps in some measure due to this wide- 

 spread use of the term by many authors that a difference of usage has devel- 

 oped. This difference of usage is nowhere more clearly expressed than by 

 Lane, 3 who says : 



"It Is to be noted that I use the term ophite, ophitic, as I have heretofore — that is, In 

 accordance with its original definition and in a narrower sense than it sometimes has 

 been used. 



"Michel Levy is responsible for the introduction of the term into petrography, and we 

 take the definition from his 'Structures et Classification des Roches firuptives,' page 26 : 



"'When 3 the last element consolidated is a bisilicate (generally pyroxenic), its 

 outlines, without their own external contours, are interlarded with other crystals ; 

 those of feldspar are notably elongated parallel to the intersection of 001 with 

 010, or are flattened parallel to 010, and the aggregate assumes a characteristic 

 appearance which I described and illustrated as early as 1877 under the name of 

 ophitic structure.' 



1 Manuscript received by the Secretary of the Society December 26, 1908. 



2 Geological Survey of Michigan, vol. vi, part 1, 1898, p. 227. 



8 "Quand le dernier element consolide' est un bisilicate (gen6ralement pyroxenique), ses 

 plages, sans contours ext€rieurs propres, sont lardees de cfistaux plus anciens ; ceux de 

 feldspath notamment s'allongent suivant l'arete pg 1 (001) (010), ou s'aplatissent suivant 

 g 1 (010), et l'ensemble prend une apparence caractenstique que j'ai decrite et desslnee 

 des 1877 sous le nom de structure ophitique." 



