26 NEW YORK STATE MUSEUM 



shell, L i n g u 1 e p i s acuminata,^ is said to be common in 

 this formation. This fixes the age of the beds as Upper Cambrian 

 (Saratogan, Ozarkian of Ulrich). 



While actual outcrops of the Theresa are few across this quad- 

 rangle, boulders from the formation are abundant along the same 

 belt and to the southward. Sometimes, as at Slab City (locality 

 41, old dam site below the bridge), and in the brook bed three- 

 fourths of a mile northeast (locality 40), these boulders from the 

 blue calcareous layers are so massed that an outcrop closely adjoin- 

 ing seems inevitable, whereas none is found. The boulders clearly 

 recognized as Theresa are usually chunky, while those from the 

 rather similar Bucks Bridge formation are frequently slabby and 

 sometimes of large area. 



Heuvelton White Sandstone 



Without any marked stratigraphic break, the lower Theresa beds 

 give place above to the " twenty-foot sandstone " of Professor 

 Cushing which according to him^ is shown by its relations farther 

 west to be merely a lentil in the Theresa, though on our meridian 

 it constitutes the apparent summit of that formation. From the 

 resistant character of this rock, and of the beds just overlying, 

 it has furnished the most important index to the rock structures 

 in the northern area. It forms extensive ledges in the Grass river 

 at Morley (locality 59) as shown in plate 7, and again on the west 

 bank below Bucks Bridge (locality 53), being responsible for the 

 water power at both places. It is conspicuous at several points 

 north of Casey Corners (localities 51, 50, 48), and three times 

 comes to the surface on Trout and Stony brooks (localities 46, 38, 

 35), besides affording the water power on the Raquette at Sisson- 

 ville (locality 31). And it is this same rock that, rising again in 

 a low anticline at Norwood (localities 19, 20), once more barricades 

 the Raquette. Westward of this quadrangle the same strong sand- 

 stone ledges appear to furnish the only conspicuous outcrops as 

 far as the Oswegatchie river, on the south bank of which they are 

 strikingly developed at Heuvelton, the type locality.^ 



^Lingula antiqua Hall, Paleontology of N. Y. i :3-4 ; pi. i, fig. 3a-e. 

 * N. Y. State Mus. Bui. 173, p. 61. 

 ' Geol. Soc. o£ Amer. Bui. 26, p. 289. 



