REPORT OF THE CHIEF ASTRONOMER 



313 



SESSIONAL PAPER No. 25a 



apatite are accessory. Quartz, kaolin, chlorite, and especially calcite are abund- 

 ant secondary products. Neither augite, hornblende, nor olivine could be found. 

 A peculiarity of this dike is the occurrence of numerous small spherical 

 aggregates of the plagioelase crystals, often mixed with quartz or calcite or 

 with both. These aggregates apparently characterize the whole dike, from 

 wall to wall. The little balls, a millimetre or less in diameter, are wrapped 

 about with mica foils, much as phenocrystic leucites, as they enlarged, have 

 often displaced small crystals of biotite in other types of rocks. The micro- 

 scopic evidence is not decisive in the present case, but seems to indicate that 

 the feldspar balls were formed during the crystallization of the rock and are 

 not due to amygdaloidal filling. An account of other ' Kugelkersantite ' may 

 be found on page 665, in the second volume of Rosenbusch's Mikroskopische 

 Physiographie der Massigen Gesteine (1907). Pirsson has described in detail 

 the ' variolitic ' f acies of a minette occurring as dikes and thin sheets in the 

 Little Belt mountains of Montana. From his description it is clear that we 

 have a very close structural parallel, in these Montana minettes, to the 

 kersantite just described. Before reading Pirsson's report the present writer 

 had independently come to the conclusion that the feldspathic ' varioles ' of the 

 kersantite are of primary origin. The fact that Pirsson had announced this 

 view in connection with the closely related lamprophyre, has given the writer 

 greater confidence in the truth of the explanation.* 



The chemical analysis (specimen No. 666) by Mr. Connor resulted as 

 follows : — 



Analysis of kersantite. 



SiO, 



TiOo 



AI 2 3 



Fe.O, 



Fe~0." 



MnO 



MgO 



CaO 



SrO 



BaO 



Na„0.. .. .. .. 



K 2 6 



H,0 at 110°C. ., 

 H,0 above 110°C. 



P,0 5 



CO,' 



Mol. 



47-42 



790 



•70 



099 



15-65 



154 



2-66 



017 



4-05 



056 



•10 



001 



4-90 



122 



8-56 



153 



•10 



001 



•14 



001 



2-60 



042 



4-10 



044 



•30 





2-60 





•54 



004 



6-24 





100-66 





Sp. gr. 



2-740 



Cf . L V. Pirsson.. 20th Annual Report, U.S. Geol. Survey, part 3, 1899, p. 532. 



