Professor Emerson on IlalVs Geological Collections. 569 



crystals a second system of lines exactly like and at rijjht-angles to tlie first. 

 This second set of lines is, however, usually only partly developed, appearing only 

 on part of the crystal or some of the lines running only part way across the same. 

 The lines themselves are generally more evenly spaced, more rigidly straight, and 

 finer than the other. In rare cases they are coarser and better developed. 

 Finally, some crystals show a beautifully i^erfect and deli(*ate lattice-work, all the 

 meshes appearing to the eye exact squares. The second set of lines runs parallel 

 to P. In agreement with this, the crystals, when examined with polarized 

 light, prove to be polysynthetically twined parallel to co P cb and O P. Some of the 

 crystals also show distinct cleavage planes parallel to the prism faces, and an 

 arrangement of the same particles in these planes. Only with a Tolles lens, of the 

 best definition and a power of 1,600, was it possible to resolve these lines into 

 their constituents. They prove to be made up of a multitude of pale-red trans- 

 parent plates, with rounded outline, which appear as black spots when in the 

 slightest degree out of focus, disappearing almost instantly, their place being 

 taken by others not in the same plane. A few elongated microlites, apparently 

 hornblende and much larger, are arranged in the same plane with the smaller 

 plates, but there is no passage from the one to the other. The small jjlates seem 

 to be hematite. The blackish-brown hornblende in broad crystals incloses much 

 well-crystallized magnetite, many hornblende microlites, also cavities with mo- 

 tionless bubbles, and is overgrown and often almost entirely changed into grass- 

 green scaly viridite, which has also passed into all fissures in and between 

 the feldspar crystals. Quartz in small rounded grains is evenly distributed 

 through the whole, and filled with fine magnetite crystals, pale-green hornblende, 

 and much smaller and longer apatite microlites, which sometimes pass with great 

 regularity from all parts of the surface of the grain toward the center. In one 

 piece long fine red needles of goethite occupy fissures. 



A few crystals of olivine and masses that seem to have arisen from its 

 decomposition occur; also minute secondary aggregations mixed with ^i^idite 

 occur. 



Magnetite occurs in large aggregations among as well as in the other con- 

 stituents. 



The minerals present in the rock in the order of their frequency are oligo- 

 clase viridite, hornblende, magnetite, quartz, hematite, ? calcite, apatite. 

 Tkap-granulite. 



Trap-gramilit. Lasaulx. Elemeute der Petrographie, p. 348. 



Diallage-grauulit. Dathe. Die Diallagcgranulite der Siiclisischcn granulit-t'ormatioii. Zeit. 

 D. g. G. xxix, p. 274, 1877. 

 A large block of a massive brownish-black trap-like rock, breaking with 



