370 J. D. Dana on the Quartzite, Limestone, ete. 
distant; and the difference we find in the Green Mountain rocks 
is only this small and often unimportant distinction made 
intensely apparent by metamorphism. 
If then a bed of rock may be quartzite in one part and mica 
schist or gneiss in another, and if these rocks alternate with 
one another in the way mentioned, there is not strictly any 
quartzite formation in the Green Mountains; for the formation 
is made up of various rocks, and quartzite is not always the 
predominant one. 
he kinds of rocks in the region under discussion have been 
here separately described with some detail because the fact 1s 
not generally appreciated that gneiss, granitoid gneiss, coarse 
and fine mica 5G hydro-mica slate, compact garnet rock, 
hornblende slate, chloritic rocks, as well as quartzite, soft an 
hard, may belong to the Stockbridge limestone formation, and 
even overlie it. Many of the rocks are precisely such as be 
long to the so-called “ Green Mountain Series,” which series 
has been pronounced on lithological evidence to be pre-Silurian 
and Huronian. 
I have collected specimens of chloritic mica slate from the 
summits of Mt. Washington in the Taconic range; of Tom 
Ball; of the Graylock ridve, near South Adams, Mass.; of Mt. 
Mansfield, in the region of the Green Mountain series of rocks 
in Vermont; and from the ridge two miles west of this city 
directly the Canaan limestone: Is the rock therefore of the 
White Mountain series and pre-Silurian? I have seen @ slate 
abounding in’ staurolites alternating with hornblende rock, 
gneiss and quartzite, in Vernon, in southeastern Vermont, but & 
few miles north of the Bernardston region of either Lower Helder f 
berg or Devonian quartzite, slate and limestone (crinoids an ne 
in diameter of stem occurring in the beds), and, as the Vermon 
Report states, the quartzites of these adjoining towns are proba- 
bly the same rock: Are these beds of the White Mountain series 
and pre-Silurian ? 
‘e learn from the facts how much virtue there is in lithology 
for determining the equivalency of metamorphic rocks. ~ 
may afford a quick answer to hard questions, but its answer '° 
worth very little unless otherwise abundantly fortified. 
: [To be continued.] 
