No. 104.] 193 



a whitish-gray color, with the component parts very distinctly 

 granular and evenly mixed throughout, containing less mica than the 

 Concord and Fitzwilliam granites, and producing one of the finest 

 building materials in the country, possessing a fine color, strength 

 and durability. 



11. 



Marbles, or Metamorphic Crystalline Limestones ; their Geo- 

 logical Position and Geographicai- Distribution. 



Crystalline limestones are everywhere interstratified with the 

 gneiss rocks of the Laurentian System, but usually forming a very 

 small proportion of the entire mass. These limestones frequently 

 contain a large proportion of other minerals, as serpentine, augite, 

 etc. ; often producing a marble of variegated character which is 

 quite ornamental. When free from these materials, it is often 

 grayish or bluish-gray, and generally coarsely crystalline. 



Limestones of this age follow the line of outcrop of the gneiss of 

 the same system, appearing to the northward in Saratoga county, 

 and extending thence with more or less continuity through Warren, 

 Essex and Clinton counties. In St. Lawrence and Jefferson counties, 

 the crystalline limestones of the same age are more extensively de- 

 veloped, and have there been known and used for a long time. The 

 same limestones likewise occur in Lewis county. In some localities 

 these limestones are cut and wrought as a marble ; but generally 

 they have only a local use, though some of them with the serpentine 

 admixture may yet prove of general commercial value. 



The white and variegated marbles of commerce are mainly con- 

 fined to the geological formation known as the Quebec group, which 

 underlies a belt of country extending from Canada through Vermont, 

 the western part of Massachusetts and Connecticut; thence into the 

 eastern part of New York, through New Jersey, Pennsylvania, Mary- 

 land, etc. 



The marbles of this group are largely quarried in Westchester 

 county; and the quarries of Tuckahoe and Scarsdale, and other 

 points, furnish large quantities of the material for buildings in New 

 York city and elsewhere. The rock is rather coarsely crystalline, 

 but compact and durable. The same marble, on the west side of the 

 synclinal axis, is quarried at Hastings and at Sing Sing, and also at 

 several places in Dutchess county. 



The formation is abundantly developed in Litchfield county, in 

 Connecticut, and at Stockbridge, Sheffield, Egremount, Barrington, 

 Alford and other places in Massachusetts. 



In its northern extension, the same formation furnishes the mar- 

 blea of Vermont, at Rutland, Southerland Falls, Brandon and other 

 places. 



Neither to the eastward nor to the westward of this formation are 

 there any extensive beds of white or variegated marble, and the 

 great sources of this material for building and ornamental purposes 

 is to be sought in this range of rocks. 

 [Assem. Doc. No. 104.] 25 



