236 Miller on the Tacontc. 
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 co- 
herent. 
He traced the rocks in a north and south course for 150 or 
200 miles, and observed the fact that they underhe the Potsdam 
sandstone, wherever it does not rest upon the gneissoid strata. 
In 1844 he pubHshed 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 the Laurentian, 
and ascertained that 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 consist- 
ing of fine and coarse slates with subordinate beds of chert, 
fine and coarse limestone, and grey, brown and white sandstone; 
these admitting however, of further divisions. The leading 
divisions recognized were: 
1. Granular quartz or brown sandstone resting unconformably 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 isolated 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, Pvitnam and Westchester counties, 
New York. 
2. Stockbridge limestone, generally known as Stockbridge marble and 
-Occuring in New York, Vermont, Massachusetts and Connecticut, 
Commencing at Sing Sing, it runs a northerly course through West- 
chester, Dutchess and Columbia counties, and extends into Connecticut. 
It passes up the valley of the Housatonic into the upper valleys of the 
Hoosic, and onward into Vermont, and is well represented at Williams- 
town, Massachusetts. 
3. Magnesian slate which composes the highest mountains in the Ta- 
conic ranges. The range of :nountains composed of this slate extending^ 
along the western border of Massachusetts and through Vermont, often 
rising to the hight of fifteen hundred feet, known as the Taconic range 
furnished the name to this system. It crosses the Hudson about thirty 
miles above New York city, and passing south through New Jersey 
enters Pennsylvania. 
4. Sparry limestone, a name given to it many years before by Prof. 
Amos Eaton. It occupies a belt of country in the eastern part of Dutch- 
