PALEOZOIC ROCKS OF THE CANTON QUADRANGLE 3I 



Middle division. The transition to the more calcareous or, 

 rather, dolomitic beds of the middle Bucks Bridge is not abrupt 

 though fairly rapid, and some heavy uniform bluish dolomites not 

 unlike the Beekmantown make their appearance. But they are 

 harder, darker and more sandy, with the " sand-crystal " cleavages 

 of the passage beds and without the soft, velvety surface of the 

 true Ogdensburg dolomite. They are exposed at but few localities 

 and their relations to the lower beds are poorly shown at most 

 of these, while their exact relation to the upper beds is still unsatis- 

 factorily determined. The best development of these layers is seen 

 (at low water) in the bed of the Raquette river just above the 

 Hewittville bridge (locality 24), where the exposures are nearly 

 continuous with those of the lower beds just upstream from them, 

 adjoining the dam (locality 26). Gastropod shells are abundant in 

 the upper surface of the bottom layer and continue frequent through 

 the 10 feet or so of beds here shown. Some of them are of large 

 size and suggest Eccyliopterus. A vitreous, white, cross-bedded 

 sandstone layer (about 2 feet thick) caps the series at the east end 

 of the bridge, and fucoidal rottenstones follow not far below 

 the bridge ; the latter being thought to correlate with the beds else- 

 where referred to the upper division. 



To this middle division belong apparently the beds formerly quar- 

 ried south of Madrid bridge (locality 8), of which the bridge itself 

 and the " twin mills "^ beside it were built. They reappear at Nor- 

 wood both above the railway bridge (locality 17) and in the brook 

 bed back of the Episcopal church (locality 18), 120 rods over on 

 the Potsdam quadrangle. On Stony brook they make picturesque 

 ledges northeast of West Potsdam (locality 2)7) > while the layers 

 at their base cause a small fall in Trout brook at locality 44. Above 



'Geol. of the 3d Dist., p. 36, fig. 2. (Hall, Pal. of N. Y. i:ii; pi. 3, 

 fig. 6). Doctor Ulrich assures me that Cleland's shell is the same as 

 the O. complanata of Vanuxem, but the " O. coimplanata and 

 O. compacta (both younger fossils) of Salter, Billings and Whitfield 

 and all subsequent authors " are not the same species but are even of 

 different genera. In this case our shell would appear to stand correctly 

 as Polygyrata complanata (Vanuxem), since the type of 

 Ophileta is clearly O. levata (loc. cit., fig. i) and not this species 

 as sometimes asserted. 



^ It is to be regretted that the reconstruction of the west m'll ^S^ar a 

 recent fire was not carried out on the original lines, hence they are no 

 lona:er twin. 



