438 
GEOLOGY OF THE FIRST DISTRICT. 
some places rest on the primary, and are slightly altered and contain crystals of the oxide of 
titanium. 
Theoretical Considerations on the Taconic System. 
It will be observed by those who have read the preceding details in regard to the Champlain 
division, and the Taconic system, that they are considered to he the same rocks, the latter 
somewhat modified in character hy metamorphic agency. This conclusion rests upon the fol¬ 
lowing trains of evidence: 
1, They are each composed of three principal masses of strata, in the same order of super¬ 
position, viz : 
^ Slate rocks; 
? Limestones; 
P Hard sandstone. 
2. Wherever we can trace the order of superposition of these rocks with Primary rocks, 
both the Champlain division and the Taconic system rest upon them, without any interposed 
strata. 
3. We have traced the changes of the slate into talco-argillaceous slate and talcy slate 
through all its gradations, and when carbonaceous, into graphic and plumbaginous slate ; the 
limestone, from compact, sandy and slaty, to checkered or sparry limestone, slaty talcose 
limestone, and granular crystalline limestones in the same continuous beds, and within short 
distances ; and the Potsdam sandstone, to a hard, compact and granular quartz rock. 
4. The localities where these changes are most marked, are situated along lines of upheav¬ 
ing and disturbing action, and where the strata have been most exposed to the influence of 
intrusive or plutonic rocks. 
These rocks, in their extremes, vary so much, that it requires very strong evidence to 
convince the mind that the rocks of the Taconic mountain range, along the line between 
New-York and Vermont and Massachusetts, are of the same geological age as those of the 
Mohawk valley; but I think that those who wdll carefully and dispassionately examine the 
subject, and who are qualifled by experience to examine a district where the geology is so 
extremely complicated, will arrive at that conclusion. 
The facts that have been detailed have not sufficient connection, and the relations of the 
particular strata and their extension have not been traced out with the care that was desirable, 
to give such evidence as to carry conviction to every mind. 
The faults and transverse heaves of the strata, and a great number of interesting classes 
of facts that it was desirable to investigate, could not be minutely studied, in consequence of 
the necessity of travelling rapidly over the country, to examine the whole territory in the 
time prescribed by law; and the facts that have been obtained, were gleaned when thus en¬ 
gaged. 
Though the facts stated may be insufficient to convince all, they, together with a multitude 
of others observed, but not noted in the manuscripts of the survey, have left a conviction on 
my mind, that the Taconic rocks are the same in age as those of the Champlain division, 
but modified by metamorphic agency and the intrusion of plutonic rocks. 
