nner 
J. B. Perry on the Geology of Vermont. 347 
suggest, viz: the true order of succession in the 
same time it should be added, that while the species in 
these successive groups are different, they still have a common 
Primordial type ; a type which distinguishes them from the 
Georgia Slate, thus indicating just what stratigraphy seems to 
beds. At 
- aganic forms of the Calciferous Sandrock, and of the several 
succeeding formations of the Lower Silurian, and thus shows 
that the Potsdam Sandstone is strictly Primordial, and may 
. be properly reckoned as Upper Taconic. 
In order to avoid all occasion for misapprehension, a supple- 
mentary remark should be made. It is sometimes urged as an 
objection, and the fact has been well known to the writer for 
years, that beds of Lower Silurian rocks are found within the 
t d 
Series of rocks than would the presence of Carboniferous 
Stata in a given district, militate against the fact of subja- 
| cent Silurian, or Devonian, formations on which they rest as 
s 
overlying beds. 
€ thus are enabled to see, on the threefold ground of 
‘thickness, of stratigraphical relations, and of organic remains, 
Sit ial, series of rocks cannot be properly regarded as Lower 
wurian in the legitimate sense of that term. The facts pre- 
“ated clearly show that the Swanton Group on which the 
= Potsdam was in places laid down, and on which it still rests, 
7 “nnot be Utica Slate or Lorrain Shales. If stratigraphy be 
of any account, it proves this in the most unmistakable man- 
ier, And, on this relationship, as I may venture to say, 
e whole matter, at least from one point of view, virtually 
“Irs. If the Potsdam Sandstone rest unconformably, as it 
Teally does, on such a series of older beds, and if there have not 
been any inversion or overlapping of the Potsdam in the locali- 
ties referred to, and there is the best evidence that there has 
3 hot, then it clearly and certainly follows that these inferior 
