LITHOLOGY. 155 
Some sections of the labradorite porphyry from Ossipee present a 
most interesting phenomenon. Many of the large crystals of labradorite 
are seen to have been all broken up after they had been formed, and then 
cemented together again. Fig. 2 on Pl. g represents one of these crys- 
tals. In this crystal, the bandings of color that are induced by polarized 
light are dislocated and out of joint, while below are pieces which have 
evidently been broken off. Other crystals in this section have been all 
broken up into a complete mass of fragments, and then all cemented 
together again. It appears in this case that the large crystal had grown 
to its full size before the mass had solidified, and at some given time a 
movement or commotion took place which broke into fragments many of 
the crystals that had been formed, and induced at the same time some 
change in condition, which caused quicker cooling and the solidification 
of the residue of the matter in little crystals. A sudden change of con- 
dition is, then, one cause which results in the production of porphyries. 
Anorthite Diabase. The diabase of New Hampshire, in which anor- 
thite has been proved to enter as an essential, is also porphyritic. The 
reasons why it should be so are of a different nature from those just 
referred to for the explanation of the structure of labradorite porphyry. 
The essential ingredients of common diabase do not widely differ from 
one another in fusibility; but anorthite fuses with difficulty, and hence, 
if it is to be formed in a mass cooling from a state of fusion, its crystals 
will have the first opportunity to grow; and where it is found in such 
rocks in our state its crystals are quite large and well formed. When 
sections are examined with polarized light, these crystals are found to be 
more or less completely altered into an aggregate of fibres, but a well 
defined centre is often left intact.. The ground mass is usually coarser 
than that of the labradorite porphyries. A good example of this rock 
is found at East Hanover, in a series of small dykes that intersect the 
slaty rocks. The anorthite is in crystals as large as hickory nuts, pos- 
sessing quite a variety of planes (see p. 90), although these planes are 
quite rough, as might be expected in such surroundings. The crystals 
are commonly altered into a translucent, waxy substance, which, as al- 
ready stated, is a mere aggregate of fine needles, and is called saussurite ; 
but often crystals with clear and undecomposed centres are found. The 
appearance of a thin section of one of these crystals is represented on 
