118 
G. T. PRIOR. 
of leucite were found by Becke in the glassy base of the trachyte from Forodada.* The 
platy felspars in this rock have a refraction a little lower, and the lath-shaped felspars 
a refraction a little higher, than that of Canada balsam. Most of the felspar is probably 
anorthoclase. 
Fig. 64. — Leucite-crystals in Base op Glassy 
Hornblende - trachyte (264), prom Obser- 
vation Hill. Tlie prismatic crystals are 
mostly augite : the long one at the top is 
hornblende. (Magnification, 150 diam.) 
Fig. 65. — Dendritic Magnetite in Glassy Base 
op Trachyte from Observation Hill. (Magni- 
fication, 200 diam.) 
Another very similar glassy variety (442) from between the ship and Observation 
Hill shows under the microscope, throughout the slide, small dendritic patches 
(see Fig. G5) of magnetite (possibly altered riebeckite or other soda-hornblende). 
A noteworthy feature of these trachytes of Observation 
Hill is the presence in many of them of dark “ lapilli-like ” 
enclosures. In the yellow rocks on the top of the hill these 
dark rounded enclosures, about the size of a hazel-nut, stand 
out on the weathered surface like fragments of black basalt 
caught up in the trachyte. Under the microscope, however, 
they are seen not to have the character of basalt, but to 
consist of a dense mesh of interlacing prisms of basaltic horn- 
blende, similar to that in the trachyte, with magnetite-grains 
and only a little interstitial felspar (see Fig. GG). These 
enclosures are therefore somewhat similar to those described 
by Becke f in the case of the similar tephritic trachyte of 
Ferrera, Columbretes. The hornblende in these enclosures 
and in the trachytes has the characters of barkevikite and shows pleochroism, a — 
yellow. /3 and y — deep reddish-brown ; the long prisms have straight extinction and 
compensate aci'oss their length with a quartz-wedge cut parallel to the optic axis. 
* Becke, 1. c. p. 176. 
t Becke, 1. c., p. 16, 8 and Taf. Ill, fig. 4. 
Fig. 66. — Hornblende-inclu- 
sions in the Trachyte op 
Observation Hill. (Magni- 
fication, 150 diam.) 
