JEFFERSON COUNTY. 
373 
General Remarks on the Primary and Sedimentary Rocks. 
The details which I propose to lay before the reader, on the geology of Jefferson county, 
will embrace the principal facts relating to the formation and characters of the lower members 
of the New-York system. I have omitted till now those characters which are founded upon 
the presence of certain fossils, having hitherto contented myself with a description of the rocks 
by their lithological characters. I have pursued this course by reason of the imperfect de¬ 
velopment of these masses in the other counties, in consequence of which they did not furnish 
so good an opportunity to bring out the peculiar characters of the inferior rocks of this system 
as do those of this county. There is, however, one exception to this remark : In Clinton 
county, the lowest of the limestones are more perfectly developed than in Jefferson. I gave, 
therefore, in the article on Clinton county, several figures illustrating the palaeontology of those 
lower limestones. My principal illustrations of this department in the geology of Jefferson, 
will begin with the birdseye limestone. The rocks of the lower series, however, are very 
well developed in this county, with the exception of the fossiliferous beds of the calciferous 
sandrock. One of the distinctive features of Jefferson is found in the great extent of the 
sedimentary rocks, or in the small extent of the primary ones. The northeast corner, con¬ 
sisting of an area of only a few square miles, and four or five narrow ridges of primary from 
St. Lawrence not extending south of the Black river, embraces the whole territory claimed by 
the Primary system. To these primary masses, require to be added some few miles of the 
same at Carthage and Alexandria bay. With these exceptions, the whole county is composed 
of sedimentary rocks, which extend from the potsdam sandstone to the loraine shales, compre¬ 
hending all those masses which compose the Champlain group, described in general terms in 
the first part of this volume. 
In the physical geography of Jefferson, we find but few prominent features. There are no 
high and commanding mountains, and the hills are all moderate ; and so far as uplifts are con¬ 
cerned in producing an abrupt and broken country, we find none. Those parts of the county 
in which the hills form a prominent feature, are the highest geologically, and become so by a 
greater thickness in the deposition of sedimentary matter, and not by an elevation of the pri 
mary, as in most other instances in the Second district. 
PRIMARY ROCKS OF JEFFERSON. 
I shall commence with the inferior rocks, the platform upon which the sedimentary ones 
are deposited, and proceed from the inferior to the superior masses ; following in this plan that 
order which nature has established, and which has hitherto been pursued in this report. 
The primary rocks of this county are granite, primary limestone, gneiss and hornblende. 
I shall not attempt to define the limits of these rocks separately, but will speak of them as an 
entire whole, except in a few instances, where the peculiarities of a particular locality require 
a specific statement. 
