384 J. D. Dana—Note on the Bernardston Helderberg Formation. 
hornblende. In other outcrops in the field adjoining, the rock is 
mostly true quartzyte, but partly a Aiea es oc hornblende 
rock, “with insensible gradations between the quartzyte. 
Again: at South Vernon, over the ae nearly west of the 
hotel, there occur—first quartzyte, but with it, and ganas 
into it, the compact green hornblende rock ; then, 
slope, a coarse garnetiferous mica schist sarang mainly of 
brown mica, which is nothing but a coarse form of the Ber- 
nardston slate: a nd in this miea schist there are hornblendie 
layers; and some beds which consist of a quartzytic syenyte, 
though with the hornblende grains in slender crystals. 
ain: between Vernon Center and South Vernon, there 
are oer showing the transition between the quartzyte and 
a quartzytic gneiss. The gneiss has the aspect of any ordinary 
light-colored thick- — gneiss. But it is all quartzytic, and 
in part very largely 
esides this fishy. polos quartzytic gneiss, there is also, 
norta of South Vernon, quartzytic syenite, a whitish rock con- 
taining small grains of greenish hornblende, rather sparsely dis- 
seminated, without mica, and making . handsome rock whic 
might at first be taken for a white erani 
5. Conelusion.—Thus, the region “affords examples (1) of the 
interstratification of the quartzyte and Bernardston mica slate, 
with a green massive hornblende rock; with a syenytic roc 
with gneiss; and with coarse mica schist; (2) of transitions of 
the Bernardston mica slate into staurolitic slate and mica schist ; 
and (3) of transitions of the quartzyte into (a) micaceous quartz- 
yte; (b) a tough quartzytic mica rock, more or less hornblendic ; 
(c) quartzytic gneiss often granitoid : (4) green hornblende rock ; 
and (5) syenyte, besides various intermediate forms. For some 
other examples of these transitions I refer to my former paper. 
emonstration is certainly complete that whatever the 
ape . the quartzyte and the associated Bernardston 1 mica slate, 
ame is the age of the rocks above mention and that 
che fossils of the Bernardston locality decide the age approxi- 
mately for the series; and tinally, that all are of the Helderberg 
formation a =i Upper Silurian, if that is true of the 
noidal lim 
6. Lithological characteristics,—In using the lithological test 
of geological age it must hence be noted that the following may 
be rocks of metamorphic Upper Silurian formations: mica slate 
and iyi staurolitiec mica poe hornblendie Aue, varying 
from a kind consisting mainly of green hornblen a quartz- 
ytic soto and hornblendie a ious gia true 
gneiss; micaceous quartzyte ; bah zyte. 
minerals included among the abundant metamorphic 
species are: brown and white mica, the former much the most. 
