178 C. SCHrCHERT THE XORTH AMERICAX GEOSYXCLIXES 



and eastern Xew York there seems to be a considerably smaller thickness. 

 In all of this we see that the Saint Lawrence trough was a subsiding area 

 from early Cambrian time to the close of the Devonian, and that nowhere 

 did more than '20.000 feet of subsidence take place. This greater sinking 

 toward the northeastern and oceanic end of the trough was accentnated 

 -by the Gaspe delta of Devonian time, where 2.000 feet of limestones and 

 T.OOO feet of sandstones were deposited. 



The seas of the Saint Lawrence trottgh at many different times con- 

 tinued confluently into the Appalachian geosyncline. Its sedimentary 

 Mstory is also far less complete than that of the Appalachian trough, and 

 accordingly the whole or the medial length of the Saint Lawrence geo- 

 •syncline was oftener dry land : at least five times was it completely 

 drained of all seas. It was dry during the Middle Cambrian and again 

 .at the close of the Caml^rian, between Beekmantown and Chazy times, 

 and again in earliest and latest Silurian times. 



It has been stated that the Saint Lawrence trough was blotted out 

 by the late Devonian orogeny. The question must be asked. Were there 

 here earlier times of folding? For three-quarters of a century geologists 

 have been pointing out the Taconic disturbance that took place toward 

 the close of the Ordovician. The area of this folding is knoAoi definitely 

 to extend from Tristates. Xew York, northeastward past Kingston to 

 IBecraft Mountain, east of the Hudson River, where all overlapping and 

 definitely ascertained Devonian strata cease. The intensity of folding 

 increases from west to east and from southwest to northeast. Tlie dis- 

 tance of known folding in a straight line is about 125 miles, and it ap- 

 pears reasonable to assume that this orogeny extends many hundreds of 

 miles northeast of. Hudson, Xew York, and to the west of the Xew Bruns- 

 wick geanticline. As yet the unconformity can not be determined in the 

 intensely folded slates of the Ordovician and Cambrian farther to the 

 .northeast. On the other hand, there is not the slightest evidence that 

 Silurian or Devonian formations were ever present on the western side 

 of the Green Mountains, but to the east, of these mountains there is 

 paleontologic evidence of late Silurian, and. in Massachusetts, of Middle 

 Devonian time. These facts appear to indicate that the eastern side of 

 the whole of the Saint Lawrence trough was folded toward the close of 

 the Ordovician. Furthermore, the succeeding Silurian deposits along 

 the southeastern side of the Saint Lawrence trough are thick deposits of 

 sandy shales and impure limestone, indicating that the Xew Brunswick 

 geanticline had l^een reelevated. In these occurrences we see that the 

 eastern portion of the Saint Lawrence trouah was folded throuohout east- 



