6 1 8 HENR Y S. WA SHING TON 



the calculated mineral composition, yielding 23.4 per cent, of 

 orthoclase and 26.3 of plagioclase, is fully corroborative of the 

 position to which Rosenbusch assigns this rock, among the 

 latites or trachydolerites. 



It would seem, then, advisable, as well as justifiable, to 

 reserve the name " kulaite" to denote a basic rock of the series 

 of latites (Rosenbusch's trachydolerites), in which orthoclase 

 and lime-soda feldspar are present in about equal amounts, 

 together making up half the rock, with nepheline to the extent 

 of from 12.5 to 25 per cent. The ferromagnesian constituent is 

 typically hornblende or pseudo-hornblende, and diopside and 

 olivine are also present. These rocks, though low in silica, are 

 essentially leucocratic in character. 



The case of the " leucite-kulaites" is rather different. On 

 the basis of chemical composition and genetic association they 

 would naturally be classed with the kulaites, as varieties of these 

 in which leucite replaces orthoclase. At the same time, com- 

 posed as they are of plagioclase, nepheline and leucite, with 

 ferromagnesian minerals, they are perfectly covered by the 

 tephrites, and in the present schemes must be called leucite- 

 nepheline tephrite. 



I have gone at some length into the question of the position 

 and names of these rocks, not because the matter is of any 

 great importance in itself, but because they serve very well to 

 exemplify the difficulties and complexities of our present 

 methods of classification. It is the old story of magmas of 

 identical chemical compositions solidifying as different mineral 

 aggregates. With the rapid increase in our knowledge of rocks,, 

 and especially through more numerous analyses and their more 

 careful execution, examples of this are becoming of quite fre- 

 quent occurrence in petrographical literature. Most cases, as 

 those of venanzite and madupite, the minette or selagite of 

 Monte Catini and wyomingite, and many more, are of rocks 

 from widely distant parts of the globe. 



Here, however, there are found at one small center recent 

 flows which must be referred to the distinct groups of basic 



