IQO ^ MINERALOGY AND LITHOLOGY. 



nearly black, on account of the preponderance of biotite. Such is a very 

 handsome granite from Newcastle. 



A specimen of biotite granite from Franconia is somewhat remarkable, 

 on account of the presence of fluor spar as one of its microscopic ingre- 

 dients. A little hornblende is also present, which has a peculiar dichro- 

 ism, being deep brown in one direction and dark blue in the other. 



A specimen from Whitefield is remarkable for its large amount of mag- 

 netite. In it quartz largely predominates, and the mica is mostly in very 

 minute grains. A specimen from Ossipee is remarkable for its large 

 content of plagioclase and microcline, and which together outweigh in 

 amount the orthoclase. It contains extremely long needles of rutile. 



Mica Hornblende Gi^anites. Granites are numerous in which both mica 

 and hornblende can be seen with the unaided eye, but the microscope 

 enlarges this class widely. In some of the mica granites a bit of horn- 

 blende is often found; but in those now to be mentioned the hornblende 

 plays an important part. 



As typical of one class of these granites, a light-colored specimen from 

 Colebrook may be described. In this granite, biotite and hornblende are 

 most intimately mixed together. Sometimes one of the black spots that 

 dot this granite will be seen under the microscope to be all of one or all 

 of the other of these minerals, but more often of both. The two minerals 

 are both very strongly dichroic, both being deep brown when the light 

 passes in one direction, and deep yellow when it passes at right angles 

 thereto. This rock contains considerable oligoclase. Apatite crystals 

 of perfect form are quite common, and some epidote is present as a de- 

 composition product. 



A number of handsome dark-colored granites, which are characterized 

 by a kind of an olive-green color, are of this class. A specimen from 

 Lightning mountain may be taken as typical. The rock is almost wholly 

 composed of quartz and orthoclase, but the orthoclase is not of the white 

 or colored opaque kind that is most common ; it is the transparent 

 variety that is called adularia. It has a very waxy lustre and a greenish 

 tint, and imparts these characters to the rock. Under the microscope it 

 is found to be much clearer, and more free from inclusions than our com- 

 mon feldspar. The quartz is of a dark, smoky color, and only on close 

 examination are grains of hornblende distinguished from it; but in thin 



