628 
GEOLOGY OF THE FIRST DISTRICT. 
in Massachusetts, and Bennington in Vermont. They are associated with rocks similar in 
character, except that the argillaceous and talcy slates are no longer recognized, and the 
associated rocks are more gneissoid, hornblendic, granitic, and sometimes trappean, than 
those in New-York above the Highlands; but not, perhaps, more than those of the Hoosiek 
and Green mountain range, of which this is an extension. 
I should never have been led to consider these limestones and some of their associated 
rocks as metamorphic, but by tracing the gradual change of character so visible in eastern 
New-York above the Highlands, and in the western parts of Vermont and Massachusetts, 
and the same changes, only more rapid, in Rockland and Putnam counties-, where the 
extensions of the taconic rocks are near the primary and the plutonic rocks; but having 
examined those transformations with some care, I have no hesitation in expressing the opinion 
that the limestones of Westchester and New- York counties are metamorphic rocks, and not 
so ancient as we have heretofore imagined. 
We have been accustomed to consider the rocks of Westchester and New-York counties 
as among the oldest of the primary rocks. It is hard to yield that opinion ; but I have per¬ 
ceived that evidence that I cannot resists that the limestones at least, and probably the 
associated micaceous gneiss, mica slate, hornblende slate, and hornblende rocks, are meta¬ 
morphic rocks, more recent in their change than the taconic rocks ; in fact, that they are the 
rocks of the Champlain division, modified greatly by metamorphic agency and the intrusion 
ef granitic and trappean aggregates. 
(B). Periods of elevation and disturbance of the strata. 
The facts accumulated on this subject, although numerous, are not such as to give all the 
certainty that is'desirable; and it is presumed that the observations made by Professors 
H. D. and W. B. Rogers, in Pennsylvania and Virginia, and which will soon be published, 
may cause some of the results here deduced to be modified. 
I have seen distinct evidences of but one period of elevation and: disturbance preceding the 
age of the fossiliferous rocks, viz : 1. That of the primary of the Highlands of the Hudson, 
and of the primary mountains of Saratoga and Washington counties, on which the polsdam 
sandstone, calciferous sandstone and black limestone, etc. repose unconformably in many 
places, though conformably in others. 
2. The earliest period of elevation and disturbance, after the commencement of the 
deposition of rocks that contain, fossil remains, of which I have seen distinct evidence, is that 
which preceded the deposition of the Helderberg limestone, which lies unconformably on the 
upturned edges of preexisting rocks, and which succeeded the deposition of the rocks of the 
Champlain division. It seems to have acted, in the First geological district, mainly through 
the Hudson valley, including the Highlands and Westchester county, and probably (if the 
veiws expressed of the age of the taconic and metamorphic rocks be true) through the Green 
and White mountain ranges, embracing most of Connecticut, Massachusetts, Vermont, New- 
Hampshire and Maine. 
