244 MINERALOGY AND LITHOLOGY, 



Plate VI, 



Fig. I. Incipient alteration of andalusite, as seen in a basal section — page io6. x 50 



Fig. 2. Complete alteration of andalusite into cyanite, as seen in a basal sec- 

 tion — page 106. X 50 



Fig. 3. Microscopic cavities as seen in a section of the olivine diabase from 

 Campton falls. The vi^alls are coated with sphccrosiderite, and prisms 

 of calcite project into the cavities which, with this exception, are full 

 of analcite — page 112. x 30 



Fig. 4. Apatite needles, as seen in a section of diabase from Bemis brook — 



pages 123 and 152. x 100 



Fig. 5. The structure of the crystalline grains which constitute ordinary lime- 

 stones, as seen in thin sections between crossed Nicol prisms — 

 page 128. x 30 



Fig. 6. Cavities common in the quartz of porphyries and granitic rocks, pages 

 i8i and 192, — very highly magnified. 



Plate VII. 



Fig. I. Augite in a section of augite sienite from Jackson. Alteration into horn- 

 blende is seen in progress, and the cleavages in the altered and unal- 

 tered portions bear the same relationship to one another as do the 

 prisms of augite and hornblende if constructed upon the same clino- 

 diagonal — pages 57 and 206. x 30 



Fig. 2. Section of hornblende schist from Cornish, showing the pleochroism of 



the hornblende — pages 16 and 61. x 30 



Fig. 3. A crystal of hornblende in a section of eruptive diorite from near the 

 Profile house. The form of the crystal is mostly filled with an aggre- 

 gate of magnetite, biotite, and calcite — pages 66 and 163. x 30 



Fig. 4. Crystals of olivine in a section of the olivine diabase from Campton 

 falls. The crystals are wholly altered into serpentine — pages 71 and 

 157- X30 



Fig. 5. A garnet in a section of staurolite slate, showing the progress of an al- 

 teration into chlorite — page 7^. x 30 



Fig. 6. A basal section of oligoclase from the Antrim granite. The section is 

 so placed, between crossed Nicol prisms, that one set of its twin lam- 

 inae is dark — page 88. x 30 



Plate VIII. 



Fig. I. Orthoclase as seen in a section of the Chocorua granite, with polarized 

 light, showing the interlamination of two parts, in which the optical 

 constants are diiTerently arranged — page lor. x 50 



