TATE: YORKSHIRE PETROLOGY. 
373 
the microscope, owning two, three, or even four descriptive titles in 
succession, indicating the opinion of the describer for the time being. 
Of these, kersanton, kersantite, minette, and mica-syenite may claim 
brief notice. " The first described Kersanton of Brest (Riviere 1844) 
and the Kersantite of the Marklode Vosges (Delesse 1851) are 
practically indistinguishable, though Delesse employed the latter 
term for Hornblende-mica-diorite, and the former for Mica-diorite ; 
while Rosenbusch (1877) restricted Kersanton to Mica-Augite- 
diorite."* Rutley (Study of Rocks, p. 239, 1877), regards the 
presence of more or less hornblende as marking off Kers:.ntite from 
Kersanton, but later he abandoned the latter term altogether 
(Proc. Geo. Ass. VII. p. 114). Minette (Voltz 1828) is applied to a 
finely grained intimate mixture of orthoclase and hornblende, 
enclosing abundant scales of mica. These rocks pass frequently into 
thefelsite series. Bonney (1884), &c. type, suggesting Minette felsite 
and Minette trachyte for the hemicrystalline and glassy forms respec- 
tively. The Minettes he regards as a small outlying group from the 
Syenites, an extreme form of the Mica-syenites; and the Kersantites 
as extreme forms of the Mica-diorites. However, not seldom is the 
determination of the felspar — orthoclase or plagioclase — in this group 
of rocks extremely difficult ; while occasionally in the series of Mica- 
traps we are having under consideration, we shall meet with examples 
in which both are found associated, iust as Rutley and Clifton Ward 
have done in the allied Mica- traps of the Lake District. The difficulty 
of determining in some cases the felspar species, in others the pre- 
dominating felspar, has led to the adoption of the comprehensive 
term Lamprophyre (Giirnbel 1879), in the sense recommended by 
Rosenbusch (1886, who used it as a convenient designation for the 
Mica-diorites, and the Mica-syenites with their intermediate members 
whether wholly or only partially crystalline. 
* M S., Geo. Lab. Museum, Royal School of Mines, S, Kensington. 
I would gratefully express my indebtedness to the Science Department, 
and especially to those responsible for the Greological Laboratory, for the 
facilities for research, without which this Bcries of papers could not 
have been attempted. — T. T. 
