PREFACE. 
viii 
that they are not found at any locality resting upon the Primary, but that the 
Potsdam sandstone is the lowest known rock resting upon that formation. The 
Taconic rocks are not found in the district that he had for examination, (2d Geol. 
district) and he has not, therefore, examined them as extensively as it has been my 
duty to do. They are found in New-York only in the First Geological District. 
Prof Hitchcock, the geologist of Massachu^tts, has also entered into a discus¬ 
sion of the age of the Taconic rocks, as they occupy some space in the western 
part of Massachusetts. His observations, and those of Prof Dana, have long since 
drawn the attention of geologists to these rocks. Prof Hitchcock has examined 
them with much minuteness in Massachusetts; and his observations, and those of 
the Profs. Rogers of Pennsylvania and Virginia, have led to some conclusions that 
tend greatly to exalt our ideas of the grandeur and great power of the physical 
causes of geological effects, and his conclusions seem to be warranted by the 
facts. Prof Hitchcock views these rocks as metamorphic, a conclusion entirely 
opposite to that of Prof Emmons ; but he could find no data from which to infer 
their age and place in the geological series. Both these gentlemen. Profs. H. D. 
and W. B. Rogers, and various other geologists, have come to the conclusion that 
these rocks, and in fact most of those from the Hoosick mountain range to the 
Hudson, have been wrinkled up and folded over, all in one direction, so as to give 
the same direction of dip; and I concur with them in this opinion. 
My own observations on these rocks and those of the Hudson valley, con¬ 
ducted with much care through their whole extent in New-York, and in Vermont 
and Massachusetts, through a series of years, have led me to the conclusion that 
they are metamorphic, and of the age of the Champlain division; that they are 
the altered limestones, slates and sandstones of that division. The evidences are 
adduced in the following work. 
The white limestone containing plumbago and various crystallized minerals, is 
another point on which there are various views. I have come to the conclusion 
that it is metamorphic, but in a more highly metamorphic state than the dolomitic 
limestones of the Taconic rocks. The facts in evidence are adduced. 
In studying the geology of this continent, both from the labors of others and 
personal observation, I have thought I recognized a great physical law sufficient 
to explain the deposition and distribution of all the sedimentary rocks from the 
oldest transition to the latest quaternary formations,; a law that still acts, and 
may be expected through all time to come to produce similar effects in the ocean, 
to those we have evidence of its having produced in times past. The discussion 
