REPORT OF THE DIRECTOR I913 65 



Raquette river. The discovery of large flat-coiled gastropods up 

 to 3^ inches in diameter in this sandstone early threw doubt 

 upon its supposed Potsdam age and led to the study of the better 

 sections on the neighboring Ogdensburg and Brier Hill quad- 

 rangles. At Heuvelton, on the Oswegatchie, the field relations of 

 the much more conspicuous ledges there widely exposed indicated a 

 position above the Theresa division, which formation shows well in 

 the falls below the dam ; and this was confirmed by the succession of 

 these strata in the nearly continuous section exposed along the 

 St Lawrence river between Morristown and Ogdensburg. The 

 heavy " twenty-foot " sandstone, carrying the large gastropods and 

 " Scolithus," was found to lie far up in the " transition " series of 

 mixed calcareous and arenaceous beds and to belong apparently in 

 the base of the Canadian group (Ordovicic), corresponding to a 

 part of what have been termed the " Tribes Hill " beds farther west 

 and south. 



The overlying, alternating sandy and dolomitic beds of the 

 Tribes Hill formation are best displayed at Buck's bridge on the 

 Grasse river and there carry well-preserved Pleurotomaria 

 hunterensis' in the sandy layers ; though farther west, as at 

 Theresa and Heuvelton, these occur in the calcareous parts only. 

 In passing eastward this formation has become far more arenaceous 

 than in Jefferson county, so much so that it too has been included 

 with the " Potsdam" in the earlier mapping. Its lithic characters 

 are here much more like those of the (restricted) Theresa beds than 

 is the case in the Theresa region, where the Tribes Hill outcrops at 

 once suggest the higher marine Beekmantown. 



What appear to be the top beds of this division are overlaid con- 

 formerly opposite the lower mills at Hewittville on the Raquette ^ 

 by 10 or II feet of more calcareous strata of different aspect. 

 These consist of drab calcilutytes, weathering light buff or 

 greenish yellow, more or less shot with irregular, brown-weather- 

 ing streaks of sand. In the Morristown-Ogdensburg section, 4 or 

 5 feet of similar beds are seen at the summit of the Tribes 

 Hill; but at an intervening exposure on Trout brook they seem 

 to be lacking though present again in a railway cut a few rods to 

 the west. The appearance of an unconformity with the overlying 

 purer dolomites of the Beekmantown at each of these three lo- 



1 Identified by Doctor Ruedemann. 

 ■2 This locality is just over the line on the Potsdam quadrangle. 



