98 The American Geologist . Fe 1 1 1 1 1 ^ : i 
Erythrite, annabergite in thick crusts, and a very beauti- 
ful bunsenite accompany the sulphides and have resulted 
from their decomposition. All these minerals were des- 
troyed in the burning of the Amherst College collection. 
Sedimentary Rocks— 'QuH, massive sandstones, with 
the finest ripple marks, red, well-bedded, pebbly sandstones, 
and buff, slaty sandstones are very abundant, and the latter 
occur also somewhat indurated and finely jointed, or baked 
masses of a thick-bedded, buff, cherty limestone. The fig- 
ure shows a curious banded concretionary structure in deeper 
shades resembling the landscape marble from Gotham in 
England. It is a distinct schlieren structure in a sediment- 
ary rock, as if a heavier layer had settled upon a lighter, and 
the latter had at stated points risen up into the former. The 
lines of flow marked by a delicate banding, and expanded out- 
wardly into a fan structure. See analysis I. 
Grey limestones with traces of brachiopods and large 
pieces of chert accompany the sandstones and closely re- 
semble the limestone of the Niagara period from the- Parry 
islands, while the sandstones have been compared by Mc- 
Clintock to the series in Byane, Martin's island, which are 
referred by Houghton to the base of the Garboniferous.* 
The sandstones here described resemble closely the New 
York Potsdam, and seem to form a fringe along the Arch- 
ean hights to the north and south of Port Foulke, as the 
former do around the mountains of northern New York. 
One large piece of the limestone has still attached to 
it a mass of chert of a pale leek-green color, of fine con- 
choidal fracture and porcellanous appearance, and many 
large pieces of the same rock occur in the collection. The 
rock resembles so exactly a compact felsyte tufa that I had 
thought it at first from its macroscopical appearance to be 
such, but its infusibility, and relation to the limestone, and 
the fact that it resembles also almost equally well slides of 
chert and hornstone, determined its reference, as above. 
Microscopically it shows a colorless, transparent, amorphous 
mass and must be largely opal. It is filled with minute, red- 
dish, non-polarizing grains, agglomerated into semi-opaque, 
often spherical, balls, which give the mass a "cumulitic" ap- 
*Jour. Roy, Dublin Society, 1857, p. 199. 
