LITHOLOGY. 203 
occurrence in the Notch, is composed of orthoclase, a little quartz, and 
many garnets, and is in composition like granulite, which, however, is 
a fine-grained and stratified rock. 
A variety from Rye is very feldspathic, but when a thin section is 
examined quartz is found, forming a cement that fills all the inter- 
spaces between the well formed and often twinned feldspar crystals. As 
an illustration of the primary formation of the orthoclase, a section of 
this rock is interesting. In Concord, just over the border, in Vermont, 
another example of exactly the same kind is found. These rocks, being 
essentially all orthoclase, furnish an example of a mineral as a rock. 
Masses of granular orthoclase in connection with granitic rocks have 
been often before observed. 
Pudding Granite. A most peculiar granite from Craftsbury, in Ver- 
mont, is included in the collections of the survey, and has been examined. 
This is a biotite muscovite granite, which contains concretions of biotite 
that are quite uniform in size, and usually about an inch and a half in 
diameter. They are spherical or spheroidal in form, and corrugated on 
the surface; and these black shining balls, scattered through the massive 
and light-colored rock, impart to it a most striking appearance. This 
granite is well known and widely celebrated as the pudding granite, a 
name indeed very appropriately suggestive. Desiring to know what 
could form the nucleus of these spheres, I sliced one of them through the 
middle, and of one half made a thin section which contained the centre. 
The interior of this concretion, as a thin section of it appears when 
slightly magnified, is represented in Fig. 4 on Pl. xi. The whole mass of 
the concretion is composed of strongly dichroic biotite, a little muscovite, 
and quartz. The section shows that it has nothing that can be called a 
nucleus, but is only a concretion of mica scales which began to be laid 
concentrically as soon as the first irregular beginning had grown suffi- 
ciently to form a basis. Zepharowich* has described such concretions, 
that occur in the mica schist of Herrmannsschlag in Austria, which in 
the interior are composed of concentric layers, as in this case ; but when 
the concretions were half grown a sudden change took place, and the 
mica began to arrange itself radially, and so continued till the growth 
ceased. 
* Mineralogical Lexicon, Austria, p. 59. 
