180 C. SCHUCHERT THE XORTH AMEBIC AX GEOSYXCLIXES 



been dry land, making its reappearance early in the Silurian (Clinton) 

 as an open marine channel depositing coarse elastics, and continuing to 

 the end of Gnelph time. These Silurian faunas are very much like those 

 •of Wales and are best known about Arisaig, Xova Scotia. During the 

 Upper Silurian the sedimentary record is restricted to its westward end, 

 the Fundy basin, laying do^vn here considerable thicknesses of marine 

 strata, but more especially great volumes of volcanic ash and lavas. 

 These center about the southeastern corner of Maine. The Fundy basin 

 ■continued with marine waters throughout Lower Devonian time, and 

 later in this period the whole of the trough was involved in the marked 

 foldings of the Acadian disturbance. 



The total subsidence of the Acadian trough apparently did not exceed 

 12,000 feet (County Antigonish, Xew Brunswick), though in the very 

 limited and highly volcanic area of southeastern Maine the total sinking 

 may have been as great as 25,000 feet. Elsewhere the deposits appear to 

 average around 6,000 to 7,000 feet. The total thicknesses are as follows: 



Feet 



Southeastern Newfoimdland (Cambrian, 2,120; Ordovician, .3,880) 6.000 



County Antigonisli, New Brunswick ( Cambrian, estimated. l.COO ; Ordo- 



vician. .5.800 : Silurian, 3,600 ; Lower Devonian. 680) 11.080 



Saint John. New Brunswick, and southeast (Cambrian, 2.1.50; Ordo- 



vician. 700 ; Silurian and Devonian, estimated. 3,500) 6,350 



Eastport. Maine (Cambro-Ordovician. 4.000; Silurian marine. 6.000; 



Silurian volcanic, 14.000 ; Devonian, 1,000) 25.000 



Eastern Massachusetts 10,000 



XOR TH UMBERLA XD BASIX 

 (See Maps, Figures 10 to 12) 



With the late Devonian orogeny, as previously stated, the Acadian geo- 

 syncline was blotted out, and then new areas of fresh water with some 

 marine sedimentary accumulation came into being. This embayment, 

 ■consisting of a series of troughs, may be known as the Xorthumberland 

 basin because it is best developed throughout the lands bordering the 

 strait of this name in Xew Brunswick and Xova Scotia. It continued 

 across the Saint Lawrence Gulf and Newfoundland, and the deposits are 

 of Mississippian and Pennsylvanian time. They average in Xew Bruns- 

 wick and Xova Scotia between 15,000 and 18,000 feet. It is interesting 

 to note that these basins of deposits lie between periodically rising moun- 

 tains, and that these mountains were reelevated four times more before 

 the whole of the Xorthumberland liasin was, in Permian times, brought 

 .above the level of sedimentarv accumulation. 



