22 TA CONIC SYSTEM. 



CHAPTER III. 

 taconic system:. 



§ 38. In 1842, Ebenezer Emmons, in his Report on the Second Geological Dis- 

 trict of New York, described the rocks lying on the sides of the Taconic Mountains, 

 parallel with the boundary line between New York and Vermont, under the name 

 of the Taconic System. He found the belt on the western border of the mountains 

 more than fifteen miles wide, and on the eastern side nearly twenty-five miles, 

 making a total width of nearly forty miles. The rocks occur in Westchester, Co- 

 lumbia, Rensselaer, and Washington Counties, and stretching the whole length of 

 Vermont, enter Canada, and extend beyond Quebec. He mentioned a typical lo- 

 cality in Berkshire, Massachusetts. The general character of the rocks was given 

 as follows : 



1. A coarse, granular limestone of various colors called Stockbridge limestone 

 from the quarries at that place. 



2. Granular quartz rock, generally fine-grained, in firm, tough crystalline 

 masses of a brown color, but sometimes white, granular, and friable. 



3. Magnesian slate. 



4. Sparry limestone. 



5. Taconic slate, which is extremely fine-grained and only slightly coherent. 



He traced the rocks in a north and south course for 150 or 200 miles, and ob- 

 served the fact that they underlie the Potsdam sandstone wherever it does not rest 

 upon the gneissoid strata. 



§ 39. In 1844 he published the "Taconic System," reviewed his former work, 

 furnished numerous evidences in support of the existence of these rocks below the 

 Potsdam and above the gneissoid rocks, or what are now known as Laurentian, and 

 ascertained they had a thickness, as shown by a single section, of more than two 

 miles. He said, taking one broad view of the whole system, it might be described 

 as consisting of fine and coarse slates, with subordinate beds of chert, fine and coarse 

 limestones, and gray, brown, and white sandstone ; these admitting, however, of 

 further divisions. The leading divisions recognized were : 



1. Granular quartz, or brown sandstone, resting uncouformably upon the older 

 gneiss. It is the least regular in its continuation of any of the rocks of the Taconic 

 System, and generally appears in insulated mountain masses, as at Oak Hill between 

 Adams and Williamstown, Mass., at Monument Mountain, in the south part of 

 Berkshire, in the east part of Bennington, Vt., and in Dutchess, Putnam, and West- 

 chester Counties, New York. 



2. Stockbridge limestone, generally known as Stockbridge marble, and occur- 

 ring in New York, Vermont, Massachusetts, and Connecticut. Commencing at 

 Sing Sing, it runs a northerly course through Westchester, Dutchess, and Columbia 

 Counties, and extends into Connecticut. It passes up the valley of the Housa- 

 tonic into the upper valleys of the Hoosic, and onward into Vermont, and is well 

 represented at Williamstown, Massachusetts. 



3. Magnesian slate, which composes the highest mountains in the Taconic 

 ranges. The range of mountains composed of this slate, extending along the western 



