i6o ALBERT JOB ANN SEN 



(2 1 1 1) Orthosyenite. This family includes syenites with ortho- 

 clase, microcline, microperthite, or anorthoclase, but with less than 

 5 per cent plagioclase. 



Orthotrachyte. The extrusive equivalent of the pre- 

 ceding. 



(2 1 1 2) Albite-syenite. A term less Ukely to be misunderstood 

 should be chosen for this family. See note under (217). 



Albite-trachyte. ' See note under (217). 



(2 1 13) Albite-monzonite. This term cannot be misunderstood. 

 See note under (218). 



Albite-latite. The extrusive equivalent of the preceding. 



(2114) Albite-monzodiorite. See note under (218). For the 

 use of morizodiorite see (2214). 



Aljbite-andelatite. The extrusive equivalent of the 

 preceding. See note under (2214). 



(2 1 1 5) Albite-diorite. This term also is unmistakable. The 

 word diorite conveys the impression of a plagioclase rock, and 

 the prefix suggests that this feldspar is albite. The term soda- 

 syenite has been used for this rock, but it was badly chosen. Soda- 

 syenite naturally suggests a syenite rich in soda feldspar, but not 

 to the exclusion of orthoclase. Albite-diorite is a much better term. 



Albite-andesite. The extrusive equivalent of the pre- 

 ceding. 



(21 16) Pulaskite Williams. This term is used in the sense 

 of Williams'^ original definition: "a rock made up of ortho- 

 clase, pyroxene, amphibole, and a little eleolite or its decom- 

 position product, analcite." In another place^ he says that the 

 orthoclase is "similar to Brogger's kryptoperthite, although the 

 amount of soda is somewhat less than is usually found in this." 

 The rock, therefore, clearly falls into (2 11 6), for while the dark 

 constituents are not prominent they are greater than 5 per cent, 

 as was shown by the examination of various thin sections from 

 the type locality. Brogger's^ type laurvikite belongs here, but the 



^ J. Francis Williams, "The Igneous Rocks of Arkansas," Ann. Rept. Geol. Surv. 

 Arkansas for i8go, II, 20. 



^ Ibid., p. 60. 



sW. C. Brogger, Die Eruptivgesteine des Kristianiagehietes . Ill: Das Gang- 

 gefolge des Laurdalits (Kristiania, 1898), p. 30. 



