﻿98 NEW YORK STATE MUSEUM 



Dip of the Paleozoic rocks 



It has just been stated that the Paleozoic rocks dip away from the 

 Frontenac axis in both directions, and it is desirable to scrutinize the 

 matter somewhat more closely. 



In the southeastern corner of the Theresa quadrangle the base of 

 the Leray limestone is at 600 feet altitude. The general line 

 of outcrop of the formation runs across the mapped area in a west- 

 northwest direction, and on the Cape Vincent sheet passes beneath 

 the river level 247 feet. This is a drop in altitude of 353 feet in 27 

 miles, about 13 feet to the mile, in this west-northwest direction. In 

 the direction of due west it is about 16 feet per mile, as nearly as can 

 be calculated. Neither one of these, however, gives the direction of 

 true dip, which lies somewhere between s. 30 w. and s. 45 w. At 

 Adams, which lies some 30 miles somewhat west of south of the vil- 

 lage of Theresa, three deep wells were drilled for gas some years 

 ago, and the records of these wells are given by Orton. 1 Fairchild, 

 who is familiar with the region, has also supplied me with data. 

 Starting on ground whose altitude is approximately 600 feet above 

 sea level, these wells reached the Precambrie at depths of 915, 950 

 and 960 feet respectively. The Precambrie surface is here approxi- 

 mately 315 feet below sea level, while at Theresa it averages' about 

 400 feet above the sea. In the 30 miles then, this surface drops 715 

 feet, or nearly 24 feet to the mile. This however is the slope of the 

 Precambrie surface, which may or may not coincide with the dip, 

 and in all probability does not. If the different limestones could be 

 distinguished in the well records the data would be at hand for deter- 

 mining the dip, but this is unfortunately not the case. If the •Paleozoic 

 rocks thicken in that direction, the dip is somewhat less than the 

 above figure ; if they thin it is somewhat greater. At Adams the 

 Potsdam and Theresa formations, 150 feet in thickness about 

 Theresa, have disappeared. The other formations are present how- 

 ever and are unquestionably thicker than at Theresa. Beginning 

 near the summit of the Trenton, the drill at Adams penetrated 

 through 900 feet of limestone before reaching the Precambrie. If 

 we knew the thickness of the Trenton in our district here we should 

 again have the necessary data, but all the upper Trenton lies to the 

 south of the map limits, and the thickness of the formation has never 

 been accurately measured so far as we know. It is certainly as much 

 as 500 feet and may be a hundred feet more than that. We have 

 then at least 800 feet of Paleozoic rocks here below the'Utica, and 

 perhaps 900. It seems therefore that the thickening of the upper 



1 N. Y. State Mus. Bui. 30, p. 457-58. 



