BY THE REV. J. MILNE CURRAN. 215 



in the coarseness and fineness of their grains, so that the last term 

 is applied to a rock which either may be holo-crystalline or may 

 retain a glassy base. It would be convenient, then, to restrict 

 the term dolerite to the holo-crystalline variety, using the epithet 

 coarse-grained or fine-grained as the case may be ; to apply the 

 name anamesite to the hemi-crystalline varieties ; and to include 

 in the term basalt all that retain a glassy base. 



The Bathurst rock I shall refer to under the name of basalt 

 simply. It is not as fine-grained as the typical anamesite, nor as 

 coarse-grained as a dolerite, and the amount of glass in the base 

 is variable. I would describe the Bathurst basalt as a blue-black, 

 compact, apparently homogeneous rock, that breaks with a 

 splintery ana conchoidal fracture, and in which the component 

 minerals can be studied only with the microscope, unless occa- 

 sionally scattered porphyritically through the mass. It occurs as 

 a contemporaneous flow and consists essentially of triclinic felspar, 

 augite, olivine and magnetite, with small portions of an unindi- 

 vidualised glassy base.* Zirkel, in studying the basalts of the 

 fortieth parallel of North America, separated the felspar-bearing 

 basaltic rocks into four distinct groups. f The Bathurst rocks 

 would naturally fall into the group which he describes as 

 "possessing a microscopically very fine-grained, totally crystalline 

 aggregation of crippled microlites, largely felspar and augite, 

 which serve as a ground-mass, in which micro-porphyritical and 

 macro-porphyritical larger crystals of felspar and olivine, with 

 occasional augites are distinctly and sharply embedded." Add 

 magnetite and occasional patches of a glassy base, and the above 

 description answers fairly well for the Bathurst rock. Of course, 

 in speaking of basalts generally, we would call our rock a felspar 



* The fact of its being a contemporaneous flow does not affect the classi- 

 fication. I agree with the English geologists who refuse to accept the 

 geological age of a rock as a character on which its nomenclature ought to 

 be based. See Judd, "On the Tertiary Gabbros," &c, of Scotland, 

 Q.J.G.S., Vol. xlii. p. 60. 



f Zirkel, Microscopical Petrography of the Fortieth Parallel ; United 

 States Geological Exploration, p. 253. 



