Faulted Region of the Mohawk. 49 



over an area of about half an acre, and the fault scarp is dis- 

 tinctly traceable in the topography for a short distance to the 

 northeast. The Calciferous appears again at Steven's mill, and 

 the overlying Birdseye and Trenton limestones are exposed in a 

 quarry a few rods east, and again at the next bridge above. 



Hoffmanns Ferry Fault. — This is the easternmost of the faults 

 on the Mohawk. It brings up the Calciferous, Birdseye and 

 Trenton formations over a wide area which extends up the river 

 to two miles above Amsterdam. The prolongation of the uplifted 

 beds so far up the river is due to exceptionally low dips and a 

 number of undulations, as in the case of the " Koses" fault in the 

 Canajoharie region. Neither the eastern front of the uplifted 

 block nor the cliffs of Calciferous -along the river gorge are so 

 prominent as at the " Noses," or about Little Falls, but they are 

 conspicuous features. A series of gentle arches in the Calcifer- 

 ous is finely exposed along the railroad and canal on the south 

 side of the river, a mile below Cranesville. The Calciferous does 

 not extend far south of the river, but is capped a short distance 

 back by a low terrace of Trenton limestone, with high hills of 

 Utica and Hudson river slate just behind. On the north side of 

 the valley the Calciferous extends up the dip to a somewhat 

 greater altitude than on the south side, and occupies a wider 

 area. Behind Amsterdam, and for some distance east, it is capped 

 by Trenton limestone in a relatively narrow tongue, which slopes 

 southward. Near the fault there is an outlier of Trenton lime- 

 stone bearing a low mound of Utica slate of small extent. To 

 the north of these areas the Calciferous is bare over many square 

 miles in a wide plateau which extends to the Sacandaga. The 

 fault plane was not observed, but its course is clearly marked. 

 It crosses the river just above the mouth of the little creek which 

 empties from the north, a few hundred 3^ards west of Hoffman's 

 Ferry. This creek flows over Utica slates which here dip 

 steeply away from the fault. A mile and a half from the river 

 the fault scarp is exhibited by thick-bedded Trenton limestone, 

 with a small showing of Calciferous below. In a short distance 

 farther the Trenton area ends, and the Calciferous gradually 

 rises into a cliff which is sharply elevated above the Utica slate 

 country eastward. The Calciferous continues for the next ten 

 7 



