﻿1 6 NEW YORK STATE MUSEUM 



The Theresa formation followed close after the Potsdam and 

 they were laid down in a trough or bay along the present St 

 Lawrence line which was landlocked on the north, south and 

 west. The depression of this trough originated to the eastward, 

 where the deposits are thickest, and deposits did not commence 

 in the immediate region until late in Potsdam time. The ex- 

 treme western extremity of the bay can not have lain many miles 

 west of the immediate region at the time of its greatest expan- 

 sion. Then it commenced to contract and slowly work back east- 

 ward. 1 



Uplift following the Theresa. This tendency to contraction 

 of the trough, caused by slow uplift of the land, seems to have 

 continued until the bottoms of both the St Lawrence and the 

 Champlain troughs had been raised above sea level, so that all 

 the northern portion of the State was above that level. After a 

 time renewed depression followed, apparently commencing simul- 

 taneously on the west, south and east sides of the Adirondacks, and 

 the Tribes Hill phase of the Beekmantown formation was laid 

 down. This was followed by uplift which began at the west and 

 worked eastward, bringing the west and south sides of the district 

 above sea level, while subsidence still continued in the Champlain 

 valley, in which a large thickness of later Beekmantown rocks 

 was deposited. This Tribes Hill subsidence came in on our dis- 

 trict here from the south and its deposits constitute the upper 

 portion of what is mapped as the Theresa formation. Until the 

 Beekmantown formation along the St Lawrence valley has received 

 further study we can not say whether the Tribes Hill limestone 

 extends east of the Frontenac axis or not. Our present view is 

 that it did not, and that the Beekmantown of the St Lawrence 

 valley represents the higher portion of the formation, deposited 

 in a trough which extended westward up the valley from the 

 Champlain basin. This depression did not carry the immediate 

 region below sea level. The district tilted to the southwest and 

 received a thin edge of Tribes Hill deposition, then rose and was 

 tilted back to the eastward, though not sufficiently to allow the 

 later Beekmantown sea of the district to the east to quite reach it. 



1 Since the field work was completed and this report written, work else- 

 where in New York has shown that probably the Theresa formation, as 

 here mapped and described, is in reality composed of two probably 

 unconformable formations, of quite different ages, and that the name 

 should be restricted to the lowermost of these, the upper being of lower 

 Beekmantown age, and equivalent to what we are calling the Tribes Hill 

 formation in the Mohawk valley. The matter is discussed in more detail on 

 a later page. 



