22 The Ta conic — Marcou. 
dug out, and in them he had observed that the slates were 
wedged into the limestone, proving their contemporaneity of 
deposition. 
The mistake of discordance of stratification spoken of by 
Emmons, is explained by the lithological and stratigraphical 
nature of the rocks; first the masses of limestone are generally 
badly stratified, being of an elliptical or ovoid form ; and second 
the slates in which they are enclosed are all strongly cleaved, 
the cleavage being very different and entirely distinct from their 
plane of stratification. 
But there is a point in the opinion of Dr. Emmons which is 
certainly correct; it is, his belief that the Taconic slates exist 
below and under those limestone masses; as it is given in his 
Whitehall section and in a part of his Bald mountain section.. 
Being lenticular masses of limestone inclosed in the Taconic 
slates, they are of course surrounded entirely by slates, and all 
the bases of the hills and mountain on which they exist are 
composed of slates, which pass under the masses of limestone 
and reappear on the other side. 
As customary, all the adversaries of the Taconic have opposed 
the observations and opinions of Marcou; and they have ad- 
hered to and adopted more or less the new "principles" sug- 
gested by Logan, in iS6i. Some disagreement in regard to 
the Quebec group, the Potsdam, and the Hudson group, has 
been expressed at different times by some of them, but in the 
main they have agreed to continue the suppression, if not en- 
tirely of the Taconic system, at least of its name, using in place 
Potsdam and Quebec, and now Cambrian [not Sedgwick's. 
Cambrian, but a Cambrian of their own]. 
The explorations of Mr. Walcott, in northwestern Vermont 
and in the area of the original Taconic, during 18S3-S4 and 
iSS6-S7,and his publications of the results obtained have changed 
the "principles" of the opponents; and we have now a third 
departure, different from the two others on many primary points, 
but agreeing in depriving Dr. Emmons of his discoveries, and 
American geological classification of its right of priority and of 
its just claims to occupy a place in the general geological no- 
menclature of the world. It is just to say that Mr. Walcott's 
opinions are far from ihe ne varietur^ for he has changed al- 
