J.D. Dana—Taconie Rocks and Stratigraphy. 209 
mass of chondroditic rock like that of Dalton. With regard to 
the age of the rest of the gneiss of the eastern borders, 1 have 
hot yet the facts needed for a positive conclusion. 
c. Between the Hastern border and the Taconic range the rocks 
of the ridges include, to the eastward, chiefly mica schist and 
quartzyte; to the westward, hydromica schist, changing to the 
South to mica schist, without quartzyte. 
" the Taconic range consists to the north of hydromica 
schist and to the south of mica schist. 
and argillyte (or phyllyte). 
J All th Saal 
metamorphic than the overlying; on the contrary, the two 
¢losely correspond in grade of metamorphism. 
- The rocks owe their positions to a system of flexures, 
and the folds or flexures are to a large extent over-thrust folds. 
The thrust was westward ;—which is proof that the pressure 
ver the limestone or over the associated schist ridges, except 
Perhaps in two eases, one in the fareast Tyringham valley, 
Mass. and the region of Monterey just west, and the other in 
South Canaan. 1 have not observed any gneiss of the kind, 
r any other true gneiss within the limestone limits north 
of southern Canaan and Salisbury. 
The quartzyte of the Hastern border is probably of Potsdam 
ye In 1872 JT pointed out that the quartzyte formation of 
ij Cughquag, in southeastern Dutchess County, lay between the 
mestone and adjoining Archean; and later, that this was 
tue of the same south of Fishkill; east of Dover and Sharon, 
At the west foot of the Kent-Cornwail Archwan range; south 
a horth of Kent, at the east foot of this range ; and I in- 
erred from the position, and apparent conformability in some 
€s, that its age was Potsdam, or that of the lowest beds of 
Silurian of the region. Similar evidence exists 
J 
on Taconic range, overlies the limestone conformably and is an 
° eal ormation; newer than the limestone. 
" this point I here add a historical note. : 
c my earliest paper on Berkshire geology, that of ests 
aco’ AWestion the direct stratigraphical evidence 
“stions, and announced the above as my conclusion. 4n my 
