440 
GEOLOGY OF THE FIRST DISTRICT. 
I believe to be the Potsdam sandstone in a metamorphic form; and the granular limestones 
associated, to belong to the same geological epoch. I believe that time will bear me out 
in expressing the opinion, that the rocks from Lake Champlain along the eastern parts of the 
counties of Washington, Rensselaer, Columbia, Dutchess, nearly all of Putnam, Westchester, 
northwest part of Rockland, and southeast part of Orange, are metamorphic and intruded 
rocks ; and I would suggest, that probably nearly all the rocks from the New-York State line 
east to the Connecticut valley are similar. The talcose and micaceous and talco-micaceous 
slates of the Green mountain range in Vermont, Massachusetts and Connecticut, have a 
strong analogy to the metamorphic slates of the east part of Washington, Rensselaer and 
Columbia counties ; but are traversed by large granite veins, and interstratified with intrusive 
rocks which might be expected to produce a greater change in mineralogical combinations.” 
In expressing the above opinion, the rocks already described as the Taconic rocks were 
included in the Metamorphic rocks. In describing the Taconic rocks separately, I have 
yielded to the opinion of some of my colleagues, who have considered them as interposed 
between the Champlain division and the Primary, I can discover no evidence of any such 
interposition, but consider them as rocks modified by metamorphic agency, and intermediate 
in their characters between the, unchanged rocks of the Champlain division, and those still 
more altered and crystalline along the eastern line of New-York, and in the western parts of 
Vermont, Massachusetts and Connecticut. 
The southern extension of the Taconic rocks across the Highlands in Putnam and Rock¬ 
land counties, will properly be considered when the metamorphic rocks of the Highlands and 
east of them shall be discussed, as some of. the limestones and other rocks are more altered 
than those heretofore described. 
The Metamorphic rocks of the First geological district may properly be divided into two 
general divisions, in consequence of the marked difference of the degree of metamorphic 
changes to which they have been subjected, viz ; 
1. Metamorphic rocks east of the Hudson, and of the Highlands. 
2. Metamorphic rocks of the Highlands, and of Saratoga and Washington counties. 
There is a marked distinction in the characters and relations of these two classes of Meta¬ 
morphic rocks. 
In the first, the limestones are granular, dolomitized, and stratified; the slates are talco- 
argillaceous, talcose, chloritic, or micaceous slates, the latter predominating; and the sand¬ 
stones are changed to granular quartz rock, eurite and gneiss. 
In the second, the limestones are changed to white and sometimes red, coarse-grained crys¬ 
talline limestone, containing various crystallized minerals, with scales of plumbago, and the 
rock rarely shows any traces of stratification; the slate is changed to mica slate, micaceous 
gneiss, or hornblende slate ; and the quartz rock is changed so as to be scarcely recognized 
as such, or compact like eurite, and is supposed in some instances to have been changed into 
some of the anomalous aggregates observed in connection with these rocks. 
In the first class, also, the intrusive rocks bear but a small proportion to the altered rocks. 
