208 Leonard Hawkes—Tridymite in Icelandic Rocks. 
Sometimes several parallel lines have a common inclination clearly 
representing a section cut across several parallel imbricated lamelle. 
Tke lamelle join at varying angles, their junction often coinciding 
with that of the quartz individuals; though two joined lamelle may 
be contained in one individual. In one case three parallel lamelle 
of one quartz are joined at an angle to three parallel lamelle of an 
adjoining quartz, at the line of junction of the two individuals. 
Again, one straight lath may be contained in two quartzes. The 
lamellas commonly have a line of dark dust inclusions along their 
middle or surface. In general there is a tendency to coincidence 
in direction of the lamelle and the length direction of the quartz 
individuals. Fig. 7 is a drawing illustrating another homogeneous 
quartz filling a cavity and showing traces of a former complex of 
tridymite tables. 
Fic. 7.—Drawing of a single quartz individual, showing traces of an original 
complex of tridymite lamelle. x 150. 
It is clear that this granular quartz of 'ype II is merely a further 
evolution of that of Type I. Taking the lamelle in the granular 
quartz by themselves, their morphological and optical characters 
exactly correspond to those of the tabular quartz of Type I. In 
a complex of tridymite lamelle the paramorphism to quartz begins 
in certain of them, many going to form a single individual or one 
being changed into several, producing the structure of Type I. 
A further step is the paramorphism of the tridymite occupying the 
interspaces between these laths, and, probably through inoculation, 
the quartz formed is in optical continuity with that already present, 
giving rise to homogeneous granular individuals. The quartz shown 
to the left in Fig. 2 is obviously in the transition stage between the 
two types. The laths are the scaffolding on which the granular 
individual is moulded. 
The question arises as to whether we have been correct in 
regarding all granular quartz in igneous rocks as primary. The 
evidence is quite conclusive that the quartz individuals of Type IL 
in the Faskrudsfjord breccia are paramorphic after tridymite, yet in 
some of them the tridymite structure is only discernible with 
considerable difficulty, and in a few it is entirely eradicated. The 
importance of this fact in questions concerning the temperature of 
crystallization of quartz is obvious, and whilst it is unlikely that 
much granular quartz has originated from tridymite in the way 
