JEFFERSON COUNTY. ;{73 



General Remarks on the Primary and Sedimentary Rocks. 



The details which I propose to lay before the reader, on the geology of JciTerson 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 count}-. 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 paleontology of those 

 lower limestones. Jly principal illustrations of this department in the geology of Jefferson, 

 will begin widi 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 

 tlie 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 primarj- 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. 



