440 TACONIC ROCKS. 



quently there must be a fault between the greater part of the Stockbridgc limestone and 

 the magncsian slates. The course of this feature we will indicate as nearly as possible. 

 Beginning at the northwest corner of Pittsford, it follows the west boundary of the Stock- 

 bridge limestone through Rutland, west of the marble quarries. There is an interruption 

 in the southwest part of Rutland, by a tongue of schist separating the limestone. This is 

 probably due to a minor transverse fault, which has thrust the limestone north of Claren- 

 don to the west of its proper position. If this is so, then, the map must be slightly 

 altered. This transverse fault may be surmised from Fig. 2, of Plate VIII ; for there the 

 belt of marble is seen suddenly to change from one side of the valley to the other. 



This lateral fault may be traced still further through Clarendon, Tinmouth, Danby, 

 west of Mt. Eolus through Dorset and through Sandgate to Battenkill River. In Danby 

 another transverse fault occurs, which does not seem to have thrust the strata to either 

 side. South of the Battenkill in Arlington and Shaftsbury, the fault is entirely in the 

 magnesian slates, west of the great mountains. The limestone does not rise high enough 

 to appear at the surface. The wearing aAvay of the magnesian slates in the west part of 

 Bennington makes the underlying limestone have of a much greater width than in the 

 towns north or south. The fault continues through the west part of Bennington, west of 

 Mt. Anthony, into the west part of Pownal. Not only are the rocks on the upper part of 

 Mt. Eolus in their original relations, but probably the westerly dip is their normal incli- 

 nation. For they were deposited upon the western slope of the hypozoic scries of the 

 Green Mountains, and dip to the west for the same reason that the rocks of the Cham plain 

 group dip east away from their nucleus in Essex County. The prevailing easterly dip of 

 the Taconic rocks is mostly unnatural. 



The next question is, what is the stratigraphical relation of the Stockbridge limestone 

 to the quartz rock ? In several places in Vermont the limestone dips west away from the 

 granular quartz, as if it was a superior rock. It is in East Middlebury, Pittsford at the 

 Furnace, in Wallingford, in Bennington, and upon the western ridge in Tinmouth and 

 Rutland. But as these cases are offset by a greater number of cases where the order 

 seems to be different, we may step over the boundary of the State three or four miles, 

 where we shall find a case of apparent naturalness in the order of strata, like Mt. Eolus. 

 It is upon Oak Hill, in Clarksburgh, and Grey lock in North Adams, Massachusetts. The 

 granular quartz rests upon the protogine of Oak Hill and dips towards Greylock. It 

 points beneath the limestone upon Greylock, and at the west base of the mountain it dis- 

 tinctly runs beneath the Stockbridge limestone. (See Plate XV, Fig. 5.) Greylock, 

 then, is composed of granular quartz, Stockbridge limestone, and magnesian slate, all in 

 their natural order apparently. 



Considering the granular quartz as subordinate to the Stockbridge limestone, then we 

 have reason for supposing the existence of another long fault, at the line of the junction 

 of the two rocks, from Pownal to Starksboro. There may not be a fault between the 

 western range of quartz rock and the limestone, for the latter may fold over the former, 

 even though the fold be inverted. 



There is some evidence in Vermont to show that the Taconic and roofing slates overlie 

 the magnesian slate, although it is rather weak, without involving theories. From 

 Sudbury to Fairhaven there is a narrow range of magnesian slate, which of course dips 



