462 PROFESSOR GEIKIE ON THE 
for example, great sheets of well-bedded trachytic tuff lie on the inner slopes of 
the crater. (See fig. 9.) 
One of the most curious and puzzling features in the contents of the tuff 
necks is the occurrence there of crystals and fragments of minerals, often of - 
considerable size, which do not bear evidence of having been formed in situ, 
but rather of having been ejected with the other detritus. Dr HEpp.e has 
noticed this fact, and has described some of the minerals which occur in this 
way. The following list comprises the species which he and I have noticed 
chiefly in the vents of the East of Fife :— 
Hornblende, in rounded fragments of a glassy black cleavable variety. 
Augite, sometimes in small crystals, elsewhere in rounded fragments of an augitic 
glass. 
Orthoclase (Sanidine), abundant in worn twin crystals in the tuffs of the East of Fife. 
Biotite, 
Pyrope, in the tuffs (and more rarely in the basalts) of Elie. 
Nigrine, common in some of the dykes, more rarely in the tuffs of Elie. 
Saponite, Delessite, and other decomposition products. 
Semi-opal, one specimen found in later tuff of Arthur Seat. 
Asphalt, abundant at Kincraig, near Elie. 
Fragments of wood, with structure well preserved, may be included here. 
In his paper on the Felspars, Dr HEDDLE has described from the neck of 
tuff at Kinkell, near St Andrews, large twin crystals of a glassy orthoclase, — 
which are invariably much worn, and preserve only rudely the form of crystals. 
He justly remarks that they have no connection with drusy cavity, exfiltration 
vein, or with any other mineral, and look as if a portion of their substance had 
been dissolved away. Internally, however, they are quite fresh and brilliant in 
lustre, though sometimes much fissured.* 
The tuffs at Elie are full of similar crystals. I obtained from one of the 
necks east of that village, a specimen which measures 4 inches in length, 35 
in breadth, and 23 in thickness, and weighs about 2 lbs. It is, however, a well- 
striated felspar. From the same tuff I procured an orthoclase twin in the 
Carlsbad form. All the felspar pieces, though fresh and brilliant internally, 
have the same rounded and abraded external appearance. 
The fragments of hornblende form a characteristic feature in several of the 
Elie dykes (to be afterwards described), and in the neighbourhood of these 
intrusive rocks occur more sparingly in the tuff. It is a glossy-black cleavable 
mineral, in rounded pieces of all sizes, up to that of a small egg. Dr HEDDLE 
obtained a cleavage angle of 124° 19’, and found on analysis that the mineral 
was hornblende.t 
Augite occurs sparingly in two forms among the necks. Some years ago, I 
* Trans. Roy. Soc. Edin. vol. xxvii. p, 223. { Op. cit. xxviii. 522, 
