Analysis of Pitchstone Porphyry from Isle Royale. 401 
*% above , C. imbricata, C. incrustans, C. foliacea. The Be- 
. renicea iveeulr of Lonsdale, and B. megastoma of M’Coy, 
~ are here 
enus SLyphadatinh Hall, p. 171.—Bryozoéid. Membranous 
or subcalcareous, growing in circular or flabellate forms, concen- 
trically or radiately striate, celluliferous on one surface only; 
frond usually a thin membrane, though often unequally thick- 
| ened and contorted or wrinkled. It is only in rare instances that 
distinct cells are visible, though in most cases the surface appears 
marked as if by stigmata or the commencement of cells, which 
sometimes pe in low nodes without presenting any defined aper- 
tures.—Sp., L. concentrica. 
Genus SAGENELLA, Hall, p. 172.—Bryozoéid. Thin membra- 
nous, net or web-like, incrusting; cells arranged in regular parallel 
or diverging series more or less oblong quadrangular when in jux- 
taposition, and separated from each other by a thin lamina of cal- 
| careous matter.—Sp., S. membranacea. 
Genus Dicryonema, Hall, p. 174.—Bryozodid, and near Fen- 
estella. Frond circular or flabelliform, wigs oe of slender radi- 
transverse branchlets; branches impressed with deep striae or 
grooves, producing indentations that sometimes have an elongated 
thomboidal form; axis subcaleareous with a corneous exterior. 
Branches sometimes like a graptolite in appearance.—Sp., D. re- 
aia D. gracilis. 
s Inocau.is, Hall, p. 176.—A plant-like corneous coral 
ith 3 basioroue bifurcating branches; structure fibrous or plu- 
-mose. The texture is like that of Graptolites, a black scaly 
crust or film being all that remains of the substance. Probably 
grew in groups of rounded or flattened stems dichotomous above. 
—Sp., I. plumulosa. 
Arr. XLVI.—Analyses of Pitchstone Porphyry from Isle Roy- 
~ ale, and of a Crystal of Phosphate of Lime from Hurdstown, 
New Jersey; by C. T. Jackson, M.D., Assayer to the State a 
Massachusetts. (Read before the Boston Society of Natural 
ty, March 19, and communicated to this Journal be the 
or.) 
te Rit 
- 1. Pitchstone Porphyry from Isle Royale, Lake Superior. 
Description. —It occurs in rounded pebbles, on the shores of 
| Wle Royale, near Scovill’s Pointg Color of the pitchstone, jet 
; lustre more rupees. than obsidian. Fracture conchoidal. 
Sp. gr. =2:375. Hardness 54. B. B. swells 7 much, exfoli- 
» Seconp cea Vol. XL yee 1851, 
