G. W. Hawes—The Greenstones of New Hampshire. 181 
The microscope furnishes as conclusive proof as the strati- 
graphy that these diorytes are metamorphic. Often in these 
basic rocks free quartz is associated with feldspars low in 
silica ; and in Stewartstown there is a dioryte in which carbon- 
ate of lime is associated with a triclinic feldspar, and also free 
lige Such circumstances as these are easily understood, if 
these rocks were consolidated under very gentle metamorphic 
influences, but would not be expected in a rock which had 
een once in a condition of igneous fusion except as a result of 
alteration. It seems as if the mass had been under such condi- 
tions of heat and pressure as to give action to chemical affinities, 
but only within a very narrow range; so that crystals of different 
minerals might be formed from fine mud, while a larger grain 
of sand would be left unaffected. The conditions of metamor- 
labradorite, making a porphyritic dioryte. At North Lisbon 
some specimens are very hornblendic, and large crystals of 
hornblende are developed in the finer ground-mass. At Lan- 
Coarse-grained and fine-grained varieties. Fig. 1, plate IV. is 
intended to illustrate the appearance of the minerals of these 
diorytes under the microscope with ordinary transmitted light. 
It is drawn from a thin section of the North Lisbon rock, and 
1s magnified 85 diameters. It shows the color of the horn- 
To Seve as a basis for calculation, the hornblende contained in 
- dioryte from North Lisbon was analyzed. In it the horn- 
oe in places had crystallized out in as orbicular masses 
alf an inch in diameter. It appears under the microscope in 
and structure like the large crystal in the section figured. 
© crystals are fringed on the edges, and consequently on the 
pure, as was proved with the microscope. A portion 
of the hornblende fee trot associated ingredients was analyzed 
following results : 
