40 E. S. Washington — New Leucite Rock. 



been hitherto unrepresented, and may be called monfi- 

 nose. As will be seen from a comparison of the norm 

 with the mode given on a previous page, the mode is 

 essentially normative, as deviations from the normative 

 minerals are of negligible amount. Using the adjective 

 m on final to denote the modal and textural (motexal) 

 characters the rock may be called monfinal monfinose in 

 the Quantitative Classification. 



In the qualitative or modal classifications also this 

 rock has been unknown up to the present. Though it 

 is, in reality, what might logically be considered a typical 

 "leucitite," yet, as has been explained above, this name 

 has a different connotation, so that the bestowal of a 

 new name is called for. That proposed is italite, mean- 

 ing thereby an effusive, porphyritic rock, composed al- 

 most entirely (80 per cent or more) of leucite crystals, 

 with minor amounts of pyroxene, glass, and possibly 

 other components. 



Formal description. — In my paper on The Roman 

 Comagmatic Region 5 there were given formal descrip- 

 tions of the various rock types, which were modeled 

 on those used in botanical and zoological publications. 

 These aimed "to give a concise, but complete, descrip- 

 tion of the type, both qualitative and quantitative, which 

 may be regarded as standard. " It is thought that the 

 use of such formal descriptions will aid greatly in com- 

 prehending the description of a rock; will render more 

 precise our ideas of what is intended to be meant by any 

 rock type or name ; and will hasten the general recogni- 

 tion of that important factor in rock classification and 

 description — the quantitative relations of the several 

 constituents of rocks, whether chemical or mineral. It 

 is, therefore, my intention to publish such descriptions 

 hereafter, whenever the occasion may arise. The tech- 

 nical terms used (for brevity) are those suggested by 

 C. I. P. AY. in their various publications, and which will 

 also be found in Volume I of "Igneous Rocks " by Idd- 

 ings. It will be noted that these formal descriptions 

 may be used whether the so-called quantitative classifi- 

 cation be adopted or not. 



Italite Monfinal Monfinose (I. 9. 1. 1.). 



Megascopic characters. — Light gray or white, equi- 

 granular or persemic, rather coarse-grained, may be 

 somewhat friable. 



6 Carnegie Publication, No. 57, p. 15, 1906. 



