432 A. P. COLEMAN 
be of a new type, and will be described here because of its inter- 
esting mineralogical and chemical composition. 
The specimens were obtained near mile 804 in a cutting on 
the railway, one being chosen to represent the freshest material 
seen, another weathered, and presenting a mottling of red and 
dark green, almost suggesting a variety of amygdaloid. Sections 
of the latter specimen are so completely weathered that little of 
its original composition can be determined ; but sections of the 
fresh specimen show that the greenish spots consist almost 
wholly of feldspars having a confused radiating arrangement 
giving spherical forms; while the red part is composed of an 
isotropic base like a clear glass penetrated by radiating bundles 
of green prisms and also larger bundles of feldspar laths, brown 
with particles of iron oxide. A little calcite scattered through 
the section proves that the rock is no longer fresh. 
The vague spheres of feldspar often have an imperfect black 
cross in polarized light, and consist mainly of orthoclase, some- 
what turbid and specked with brown iron oxide, with a little of 
the green mineral intermixed. The rest of the rock contains 
some orthoclase also, but consists chiefly of the isotropic substance 
inclosing the radiating bundles of prisms referred to before. 
The green prisms are fresh in color and appearance, and are 
usually distinctly dichroic, dark green when the prism is parallel 
to the chief section of the nicol, yellowish-green at right angles 
to this position. Extinction is nearly parallel, but angles of 4% ° 
occur. The larger crystals sometimes have sharpened ends, 
The mineral was at first taken for hornblende, but is no doubt 
aegyrite. : 
The other mineral forming radiating bundles is probably 
plagioclase, clearer parts showing twin lamellae, whose angle of 
extinction, however, could not be sharply determined owing to 
the small size of the lamellae. Many of these plagioclase strips 
are reddish-brown and almost opaque, with particles of brown 
iron ore. 
The only other primary mineral observed, except a few 
needles of apatite, is the isotropic base in which the crystals 
