PALEOZOIC ROCKS OF THE CANTON QUADRANGLE 25 



crops, to the quarries of the type red Potsdam sandstone below 

 Hannawa Falls (on the Potsdam quadrangle). 



Between the Raquette and the Grass are found only occasional 

 small sometimes doubtful exposures of the Theresa beds, usually 

 immediately beneath the Heuvelton ledges (localities 45, 48, 49, 

 42?). Of these, the most interesting is that at locality 42, West 

 Potsdam, already described. On the Grass river just above Morley 

 a rather strong anticline brings up these beds, chiefly in the river 

 itself and on the west bank above the cemetery (locality 61 ; com- 

 pare figure A of plate 7). Immediately below the Morley bridge 

 (locality 59) they are again unroofed for a few rods on the west 

 side of the stream. Finally the latter phenomenon is repeated 

 one-fourth of a mile below the ruined dam at Bucks Bridge, where 

 typical Theresa strata are seen on the east bank in a little slough 

 (locality 52), Much better exposures occur on the Oswegatchie 

 river above Heuvelton, several miles west of our map. 



The rocks of the Theresa formation are generally blue-gray when 

 fresh. This color is usually retained, on weathering, by the strictly 

 calcareous layers, while the sandy portions turn either ashen or 

 more commonly brownish. On long rotting, the color deepens to 

 a chocolate and the beds become very weak; but the calcareous 

 layers may slowly dissolve away without rotting. Calcite is the 

 cementing material throughout, so that fresh specimens foam freely 

 in dilute acid. The gleaming surfaces described by Gushing, due 

 to cleavage of this crystalline calcite cement, are frequently seen 

 on fresh fracture, and are usually slightly warped or curving ; but 

 these occur also in higher strata. 



The stratification in the Theresa is crude and irregular; usually 

 not in very heavy beds. Small lentils or pockets of the soluble blue 

 limestone show at intervals throughout the sandy layers, which are 

 inclined to be crudely cross-bedded, while stringers and knots of 

 sand break the calcareous portions. Pittings of the size of a finger 

 tip frequently develop on the weathered surfaces of the coarsely 

 sandy streaks. In general these rocks tend to become very cragg}' 

 on exposure, furnishing an admirable foothold for mosses and 

 small herbs. 



No organic remains have been found. The pittings above men- 

 tioned are the surface expression of tubular chocolate-colored 

 stains extending irregularly through the rock in f ucoidal fashion ; 

 but whether these are really of organic origin (burrows or alga 

 stems) remains to be determined. In Jefferson county^ a brachiopod 



'N. Y. State Mus. Bui. 145, p. 65. 



