Geology . 419 
Primitive Trap. — This is the pure black hornblende, 
the hornblende slate, and the mixed hornblende ; it appears 
at 11 and 12 miles from Philadelphia on the Chesnut 
Hill road immediately after the steatite or soap stone ; and 
intermingling with the micaceous shistose limestone,, and 
then with the granular limestone. 
Granular Limestone. — Crystallized : this may be ob- 
served on the road to White Marsh, about 13 miles from 
Philadelphia : the mica slate, becomes gradually mica- 
ceous limestone slate, and then granular limestone or 
marble, coloured with hornblende (amphibole, primitive 
trap) as in the black, and black and white marble of 
White Marsh used at Philadelphia. The clay slate here, 
does not intervene so far as I recollect. 
Serpentine. — I have not traced this in the neighbour- 
hood of Philadelphia : the soap stone first appears. This 
I think 'passes into serpentine, of which the neighbourhood 
of Easton famishes fine specimens. Chlorite escaped me. 
Porphyry and Sienite. — Porphyry, is compact feldspar, 
containing small crystals of feldspar : or quartzose stones 
containing such small crystals. Sienite, is a stone com- 
posed of feldspar, quartz and hornblende. I suspect this 
formation has not been traced upon, or over lying the ser- 
pentine in Pennsylvania. These stones abound, as rolled 
specimens out of place, on the shores of the North East 
branch of the Susquehanna from Danville upward to 
Wilkesbarre, and I believe atintervals as far as Tioga point. 
1 know not the source of them. I suspect them to belong 
to the secondary trap formations, for they are intermixed 
with all the varieties of green stone. The feldspar is ge- 
nerally reddish. 
Sometimes a second deposition of granite, or newer, 
more recently deposited granite, is found among the pri- 
mitive strata :■ in this the crystals are similar to those of 
Vo L. III. 3 F 
