504 



/. H. OGILVIE 



ited the cubical cleavages of analcite. The rock was fresh and 

 this mineral was undoubtedly of primary origin, being appar- 

 ently the last to crystallize and filling all interstices. The larger 

 grains are free from inclusions, but are sometimes surrounded 

 by rings of magnetite and ilmenite grains ; the smaller grains 



often contain a fine 

 black dust suggest- 

 ive of leucite. This 

 structure appears to 

 be identical with that 

 described by Mr. 

 Cross in the case of 

 an analcite basalt. 1 



Magnetite and 

 ilmenite are abund- 

 antly distributed in 

 large crystals. Apa- 

 tite occurs in the 

 form of elongated 

 prisms with trunca- 

 ted corners, and is 

 common throughout 

 the groundmass. 



Very little alter- 

 ation could be seen in any of the constituents. As already 

 mentioned, very small amounts of secondary hornblende occur, 

 derived from the augite. The plagioclase is occasionally slightly 

 sausuritized, and small quantities of secondary epidote are occa- 

 sionally found. The rock as a whole is, however, remarkably 

 fresh. 



The most noted district for rocks of this class is the neigh- 

 borhood of Lake Champlain, where they have been made known 

 principally through the work of Professor Kemp. 2 The writer 



1 Whitman Cross " An Analcite-basalt from Colorado," Jour. Geol., Vol. V, 

 1897. 



2 J. F. Kemp, "Trap Dikes of Lake Champlain," Bull. 107, U. S. Geol. Surv. 



Fig. 3. — Intergrowth of hornblende and augite, 

 with inclusions of augite in hornblende. 



