

( 



! 



NEW ENGLAND APPALACHIAN SYSTEMS 



187 



SOUTH 



NORTH 



Fig. 11.15. North-south section in north- 

 western Vermont of the Cambrian and 

 Lower Ordovician formations, restored to 

 early Ordovician. Reproduced from Shaw, 



1958. 



OUNHAM DOLOMITE 

 MIOOLEBURY SYNCLINORIUM 



FRANKLIN BASIN 



OUARTZITE 



DOLOMITE 



SLATE 



LIMESTONE CONGL. 



Taconic belt and northwest of it is the undeformed shelt sediments which 

 lay onto the Canadian Shield. 



Stratigraphij. The stratigraphic columns presented in Fig. 11.14 are 

 by Cady ( 1945) and represent a long endeavor by numerous geologists to 

 unravel the succession and to correlate the different formations in the 

 region. As previously noted, it appears that two lower Paleozoic succes- 

 sions of approximately equivalent age exist within the same area, and 

 1 the tendency of most workers is to regard the argillaceous sequence as an 

 allochthone from the east now reposing on a calcareous western sequence. 

 The Cambro-Ordovician limestones and dolomites grade westward into 

 foreland sandstones of the Adirondack area, and, it is believed, eastward 

 into shales of geosynclinal thickness. Cambrian and early Ordovician 

 sandstone tongues extend far to the east. The geosynclinal trough mi- 

 grated westward later in Ordovician time and resulted in the deposition 

 of a shale facies over, and in places uncomformably on, the calcareous 

 and sandy succession. This was the occasion of the Vermontian disturb- 

 ance (Kay, 1942). 



Kay's (1942) map of Fig. 11.11 restores the distribution of Lower 



Ordovician strata in the region. He names the eastern trough in which the 

 shale facies was deposited, the Magog; a postulated barrier to the west. 

 the Quebec; and the shallower trough in which the carbonates were de- 

 posited, the Champlain. 



In the St. Alban's area of northwesternmost Vermont, north of Cady's 

 mapping, Shaw (1958) reports some unexpected facies changes in the 

 Cambrian and Lower Ordovician along the structural strike. These are 

 illustrated in Fig. 11.15. A northern basin, the Franklin, was partially 

 restricted from a southern bv an east-west high, the Milton, and streams 

 carried considerable clastic material into it from the Adirondack and 

 Laurentian land area. Throughout Cambrian and Early Ordovician times 

 the basin was one of considerable crustal unrest, as evidenced by the 

 several unconformities. 



Structure. Although considerable doubt exists about the Taconic 

 klippe hypothesis south of Albany, there seems Little question in the 

 minds of those who have worked in the Lake Champlain lowlands about 

 the reality of major cast to west thrusting. 



A number of thrusts other than the great Taconic thrust, but of the 



