C. H. Smyth, Jr. — Peridotite in Central New York. 328 



" Uplifts of tlie Mohawk,"* and is spoken of in the papers 

 above cited, though never visited by the authors. 



The fault, which involves the strata from Archaean to Utica 

 slate, is plainly shown at the highway bridge over the East 

 Canada Creek, a short distance north of the railroad. Here 

 the Utica slate forms a wall ten feet high on the east side of 

 the creek, while the corresponding western wall, about eight 

 hundred feet away, is Calciferous sand-rock. The strata on 

 both sides are horizontal, but as the contact between the two 

 formations is covered by stream deposits, there may be, and 

 probably is, a flexure of the rocks near the fault. The strike 

 of the fauit is about IN". 20 E., coinciding with the direction of. 

 the valley. One mile farther up stream the strike of the fault 

 changes to JN. 40 E. crossing the stream, and thus producing a 

 considerable fall, the sand-rock here rising above the slate in a 

 bluff over one hundred feet high. At this point, the contact 

 between the sand-rock and the slate is shown, and there is a 

 marked disturbance of the latter. Two hundred feet back 

 from the fault the slate begins to bend slightly upward, and 

 the inclination rapidly increases, till at the fault the dip ap- 

 proaches 90°. At the same time, the flexure brings to view 

 the underlying strata of Trenton limestone. As would be ex- 

 pected, the thick bedded calciferous sand-rock on the upthrow 

 side is much less affected, being bent downward very slightly. 



It is at this point, near the foot of the falls and on the east 

 side of the creek, that the dike occurs, filling a space ten 

 inches wide in the plane of the fault between the sand-rock 

 and the slate. In connection with the dike is a one inch vein 

 of caicite carrying galenite and pyrite, and some fifty years 

 ago, with a view of working this vein, a drift was run in about 

 sixty feet, when the dike pinched out, In the opposite direc- 

 tion the dike passes under the creek and does not extend to 

 the west bank. It is, therefore, not more than one hundred 

 and fifty feet in length. However, it seems probable that the 

 rock exists at other points along the fault, being covered by 

 drift. 



The rock is granular and of a dark green or gray color, with 

 a mottled appearance due to the presence of a light green, to 

 white, mineral. Scattered through it are abundant plates of 

 dark brown mica, often 6-8 mm in diameter. The appearance 

 of the rock varies but slightly, excepting when it has been 

 weathered. In the latter case the product is a light yellow, 

 pulverulent clay, with scales of mica scattered through it. 

 Microscopic study shows the rock to be made up largely of 

 olivine, with less mica, in a ground mass chiefly crystalline. 

 The porphyritic structure is distinct and constant, with but 



* Geology of New York, Part III, pp. 207, 208. 



