PALEOZOIC TIME — LOWER SILURIAN. 531 



into New York (or Manliattan) Island. The limestone, which is everywhere 

 crystalline, or is a marble, contains abundantly the same accessory minerals 

 in southern Massachusetts and Connecticut, as in Westchester County and 

 New York Island ; namely, tremolite and white pyroxene. In this respect 

 the Taconic limestone is widely different from the Archsean limestones of 

 the protaxis in Massachusetts, and of outcrops in the Kent-Cornwall Ridge, 

 west of Kent, these being chondroditic (p. 67). 



Two of the Westchester belts, near Peekskill, extend northward up the 

 Archaean Highlands of Putnam County. They lie in what were originally 

 valley-depressions in the Archsean, although not valleys now. Their beds 

 are much upturned, although confined so closely by the Archaean ; and they 

 are metamorphic, but of the lighter kind characterizing the corresponding 

 beds on the north border of Peekskill. To produce the upturning, the 

 inclosing Archsean rocks must have been thrust forward either along frac- 

 tures, or molecularly. The metamorphism apparently indicates that the 

 beds once had great thickness over this part of the Highlands. 



The Taconic series of rocks, and series of upturnings, appear therefore to 

 extend all the way from the St. Lawrence valley to New York City. They 

 are situated mostly to the west of the Archsean protaxis ; but, in Canaan, the 

 more eastern branch, described above, passes to the eastward of it, leaving part 

 of the Archsean area on the west ; and it is this eastern branch that continues 

 on through Westchester County. The east and west positions of part of the 

 limestone belts of Westchester County, just south of the Archsean of Putnam 

 County, indicate that, in the upturning, the schists and other Taconic rocks 

 were forced up against the essentially stable Archsean area. The T-shaped 

 symbols on the map indicate the strike and dip of the rocks, and show 

 that the limestone and schists, referred to the Taconic series, are conform- 

 able in strike. 



The Taconic upturning is known to have occurred not later than the close 

 of the Lower Silurian era from the fact that Upper Silurian rocks are not 

 present in the series, btit actually overlie the Lower unconformably in some 

 localities; as at Becrafts Mountain, near Hudson, N.Y. ; on St. Helens Island 

 and Beloeil Mountain, near Montreal, where the Lower Helderberg beds cover 

 unconformably Lower Sikirian slates ; and near Lake Memphremagog, where 

 the Niagara limestone occurs with its characteristic fossils, and also beds of 

 Devonian Corals. Again, on the eastern side of the Green Mountains, in the 

 Connecticut valley, there are unconformable Devonian beds at Bernardston, 

 Mass., and Upper Silurian at Littleton, N.H. The earlier of the formations 

 of the Upper Silurian are very thin in the eastern part of the state of New 

 York, and this is apparently owing to the previous emergence of the Green 

 Mountain area, shallowing the waters to the eastward. The schists, which 

 are argillyte and hydromica schist in Vermont, are mica schist, chlorite schist, 

 and gneiss in Massachusetts, and coarser mica schist and gneiss in West- 

 chester County. 



The probability that the upturning was continued southward through 



