GEOLOGY OF OGDENSBURG 3/ 



No such beds as these have been seen anywhere on the Brier 

 Hill quadrangle, and they are believed to be totally absent there. 

 It is quite possible that they may exist on the eastern half of the 

 Ogdensburg quadrangle, but no outcrops have been seen, and they 

 are probably wholly covered by drift. 



The middle division consists of more massive, less sandy beds, 

 some of which are blue and strongly dolomitic, suggesting the 

 character of the overlying Ogdensburg formation, though every- 

 where more sandy than the Ogdensburg beds. These beds have a 

 thickness of some lo feet, and are capped by a hard layer of white 

 vitreous sandstone. Fossils are most numerous and varied in this 

 division. 



The upper division consists again of thin-bedded, fucoidal, sandy 

 and siliceous dolomites, quite similar to the beds of the lower divi- 

 sion, but more magnesian and less calcareous. They also contain 

 fossils, but less abundantly than the middle division. They have a 

 thickness of at least 25 feet. 



In the Raquette river section, at Hewittville, Professor Chadwick 

 finds an additional thickness of some 9 feet of somewhat argil- 

 laceous, firm, fine-grained, light-gray limestones and dolomites, with 

 sand grains only in streaks, quite different looking beds from the 

 Tribes Hill beneath, and lying beneath the Ogdensburg beds. They 

 have furnished no fossils. They seem to wedge in toward the east 

 and to be absent in the remainder of the district. It may be 

 suggested that here is the extreme westerly edge of that portion of 

 the Champlain Beekmantown which underlies the Ogdensburg divi- 

 sion in those sections. 



Ogdensburg Formation 



General statement. As has been stated in the preface to this 

 report, the study of the Beekmantown formation of the region was 

 the principal object of the field work. The other formations appear- 

 ing were known to be those which had already received detailed 

 study elsewhere. But none of the Beekmantown of New York 

 has ever been studied in the desirable detail requisite to furnishing 

 a good idea of its history and its fauna, and almost no study what- 

 ever had been previously given in the State to the formation as 

 shown in the St Lawrence valley. It was known to be less fully 

 shown here than in the Champlain valley, and we had predicted 

 that the lower beds would be absent, on the basis of the belief 



