1884.] The Crystalline Rocks of the Northwest. 995 
III. Below this great mass of soft schists, he described, in the 
first place, a mass of 500 feet of limestone, designated “ Stock- 
bridge limestone,” which graduates downward into “talcose” or 
magnesian sandstones and slates, the whole having a thickness of 
about 1700 feet. à 
IV. Under this limestone is his “ granular quartz rock,” more 
or less interstratified with slates, and becoming, in some places, 
an immense conglomerate with a “chloritic paste.” In this con- 
glomerate are fragments of the underlying gneiss, or 
V. A formation which constituted, in his scheme, the “ ancient 
gneiss” on which the Taconic system was said to lie uncon- 
formably. , 
Now it requires but a glance to perceive how closely this order 
coincides with that which has been independently and laboriously 
worked out in the Northwest. We have in both instances a 
“black slate” which in one case is said to be at the top of the 
system, but to pass apparently beneath the “ancient gneisses,” 
and in the other is reported to be overlain by a group of mica 
schist and the “ youngest Huronian,” a mass of gneiss and gab- 
bro. Below the black slate in both cases is an immense series 
of soft, hydro-mica and magnesian schists. These again are fol- 
lowed by limestone which in the Northwest often forms marble, 
and in New England sustains extensive marble quarries. This 
has various transitions to slate and to a hard sandrock, but in 
both places it becomes known, in its lower portions, as a great 
bed of quartzite ; and finally at the base is coarsely conglomeritic 
Vith masses of rock from the great underlying series of gneiss. 
Were there no other precedent this very parallelism would at 
once be taken as demonstrative, or at least indicative, of equiva- 
lence of age. The “Stockbridge limestone,” however, at Stock- 
ridge, seems to be of the Trenton age, according to Professor 
Dana; and where it appears in the Taconic mountains, farther 
South and west, it is assumed by him to be of the same forma- 
tion. But no one can affirm safely that the Taconic range of 
Mountains is made up of the Trenton and Hudson River forma- 7 
tions till the crucial test has been applied to them successfully in 
the discovery of the characteristic fossils, and assuredly not, in 
the absence of this test, in the face of the foregoing parallelism 
with a limestone Soe to lie much lower ; and in the face of the 
discovery of primordial fossils in Bald mountain some miles fur- 
VOL. XVII.—NO. x. 63 
