Cam.jytonite Dikes. — Marsfers. 369 
rocks are composed of white crystalline limestone, and further 
west they consist of calcareous and talcose schists. The lime- 
stones in the early reports on the geology of Vermont are 
designated as the Eolian limestones. 
On the western flank of the valley in a southwesterly di- 
rection from the village were found two abandoned quarries. 
These openings are probably the Syminyton or Fisk quarries 
mentioned in one of Hitchcock's early reports as being inter- 
sected by dikes. 
In the upper quarry were found two dikes cutting the lime- 
stones in a direction approaching N. 47*^ E. and N. 30" E., 
about one thousand feet apart and with a thickness of one 
and five feet respectively. 
The dikes are characterized by a hypidiomorphic structure, 
dark gray in color when fresh, but rusty brown in the weath- 
ered outcrop. Although the greater part of the rock is very 
fine grained, minute lath-shaped crystals can be seen in the 
hand specimen without the aid of a lens. Scattered through 
the rock are numerous minute pockets or cavities filled with 
a white mineral substance. In some instances these prove to be 
calcite, in other (as noted in the thin sections) they consist 
of minute aggregations of feldspar crystals. 
Microscopic examination proves these rocks to be made up 
of idiomorphic hornblende of the basaltic type, augite in two 
generations, small amounts of plagioclase, and more or less 
glass in the interstices of the ground mass. Although this 
mineral mixture is regarded as a Camptonite, it nevertheless 
differs in some respects from the Campton Falls dike, which 
is regarded as the type. The "Danby" occurrence differs from 
the type in exhibiting but one generation of hornblende. Not 
a single large phenocryst of hornblende has been found in the 
several sections made from each dike. The form present is 
lath-shaped with ragged terminations, and is identical with 
the hornblende of the second (jeaerntion, as noted in the Camp- 
ton dikes. The pleochroism, ranging from light yellow to deep 
reddish brown, is unusually strong. Numerous cross-sections 
were noted in which prismatic and pinacoidal faces were eas- 
ily recognized and in some instances the crystals were sutH- 
ciently large to show clearly the characteristic prismatic 
cleavage. 
