572 Professor Emerson on HaWs Geological Collections. 



divisible into two groups, large and small, respectively, about ^ and 2 times as 

 large as in No. 101. Decomposition has not proceeded so far, the crystals being 

 quite translucent, of a faint ocher-yellow color, and in large part isotrope. One 

 of the larger and many of the smaller show perfect eight-sided cross sections. 

 Manj^ of the larger crystals are grown together in groups of two and three, a little 

 more than half of each being present. The larger crystals are affected in various 

 ways bj' decomposition ; some have the center clouded with ocher-yellow, bounded 

 by a clear ring, and this by a ring of blood -red rubellan in minute closely aggre- 

 gated crystals, which project into the clear ring. Others having the exterior 

 ring of rubellan are in the interior clouded more or less with a green material. 

 In others this green material is gathered at the center, having a clear yellow 

 area between it and the outer ring of rubellan. In others a pale grass green 

 spreads over the whole, and finally the whole crystal is changed into a bright 

 grass-green viridite, arranged in wavy masses, which recall the fluidal structure 

 of obsidians. Cyanite occurs in smaller crystals than in Xo. 101, with rectangular 

 cross sections. It polarizes brilliantly. Magnetite is abundant. The contrast 

 of the bright green of the viridite, the deep blood red of the rubellan upon the 

 pale amber background of garnet, makes this a ^'ery beautiful object under the 

 microscope. 

 104. Trap-granuute. 



This rock is like No. 101 in appeaiance, and came probably from another 

 portion of the same mass. It is, however, much more weathered and pitted super- 

 ficially by the eating out of calcite, which had filled cavities in the rock. Eounded 

 grains of quartz project from the surface. Many of the cavities are not wholly 

 emptied, there remaining a soft pulverulent mass, which efi'ervesces freely with 

 acid and is wholly dissolved. Black needles of hornblende, like the calcite of 

 secondary origin project into the latter. With tlie lens one sees, especially 

 when the rock is moistened, rubellan, hornblende and light gray spots, which 

 resemble the flesh-colored ones seen in No. 101, and which are, as in that case, 

 garnet. 



The whole rock efl:ervesces abundantly with acid, irnder the microscope 

 the section is much clearer, the rubellan more scattered and in larger crystals, 

 the rest more uniform and homogeneous in appearance than in No. 101. The 

 ground color is pale ocher-yellow, clouded with darker shades of the same color. 

 The ground shows distinct traces of tesseral forms, and remains dark under 

 crossed Nicols. In tlie mica small transparent garnets occur. Tlie rubellan 

 occurs in large clear pieces deep blood-red and dark orange, inclosing, (besides 

 garnets,) hornblende, and needles of apatite; and often bordered by magnetite. 



