FAULT A-A. 289 



the brook turns at an abrupt angle into the fiiult line, to Chazy village, 

 where the brook joins the T.ittle Chazy river. Beyond Chazy village the 

 river leaves the fault-line, but the railroad closely follows it to the town- 

 ship line. The fault can be first recognized north of West Chazy, where 

 the road crosses Tracy brook, and here ledges of Potsdam sandstone are 

 exposed on the west side of the stream, while only a few rods away to 

 the east, with verr diflerent strike, are beds well down in the lower 

 division of the Chazy. To the south the further extension of the fault 

 is concealed by a heavy covering of drift. To the north, however, it is 

 readily traceable througliout the township. The heaved block on the 

 west brings Potsdam sandstone to the surface in all outcrops. On the 

 east the thrown block is much broken, especially in the vicinity of Chazy 

 village, so that ledges of varying age abut against the fault-line, the range 

 being from the lower Chazy up to the Black River limestone. Every 

 vestige of the Calciferous is faulted out. This fault is traceable, with 

 a great degree of pro])ability more than half way across Chami)lain 

 township next north of Chazy, giving it a known length of from eleven 

 to twelve miles. In that township the Calciferous comes in, conformably 

 overlying the Potsdam, on the west side of the fault. 



The vertical throw of this fault cannot be accurately determined, owing 

 to lack of knowledge concerning the thickness of the Calciferous here. 

 Brainard and Seeley have shown that at the upper end of lake Cham plain 

 the Calciferous has a thickness of 1,800 feet, and that, while toward the 

 lower end of the lake no complete exposures are found, the different 

 members of the formation hold their thickness pretty persistently.* If 

 this is assumed to be its thickness here, the fault has a throw of about 

 2,0(X) feet at Chazy village. The character of the rock exposed there on 

 the west side of the fault is that of the passage-beds between the Potsdam 

 and Calciferous, while on the east side are beds of the lower division of 

 the Chazy, so that the throw of the fault is not much in excess of the 

 thickness of the Calciferous. 



In their work at Chazy village Brainard and Seeley recognized this 

 fault and fully realized its importance.! Though they did not attempt 

 to plot it or trace it for any distance, their map indicates its course for a 

 mile and a half southwest from the village. The fault was also recog- 

 nized by Mr Walcott when there, though he seems to have regarded its 

 throw as of small amount and accounts otherwise for the non-ai)pear- 

 ance of the Calciferous. J 



Ffif'lt C-C — At a varying distance; of from one to two miles east of 

 fault A-A is another great north-and-south fault, roughly parallel with it. 



• Bull. Am. Mu«. Nat. Hint., vol. IH, no 1. pp. 1-2.3. 



t Am. Geologist, November, 1888, p. 3i!7, an«l Hull. Am. .Mus. Nut. HIh., vol. iii, no. 1, p. 13. 



J Bull. 30, U. S. Geol. Surv., p. 24. 



