GEOLOGY OF OGDENSBURG 39 



Gray, granular dolomite, capped by a 3-inch layer of 

 dark blue, magnesian limestone which contains many 

 gastropods ; the 3-inch layer is solidly welded to the 

 gray bed beneath. 



2. 13' 



Dark blue, sandy limestone, very full of rounded 

 quartz grains, wath calcareous cement showing frequent 

 '' sand crystal " cleavages ; nearly half of the rock con- 

 sists of quartz sand. 



12' 



Gray dolomite, with frequent sand grains, and with 

 some calcareous cement. 



These appear to be the very basal beds of the formation. The 

 contact does not show here, but undoubted beds of the Heuvelton 

 calcareous sands come in not far below and, as the Ogdensburg 

 beds are more resistant to erosion, it is probable that this is the 

 very bottom. The sand grains in the two lower layers show that it 

 is near the base, at least. Furthermore, outcrops of the tipper 

 Heuvelton in the road gutter, a short distance to the west, show 

 a slightly irregular upper surface, in the depressions of which are 

 patches of sandy dolomite, which are precisely like the basal bed 

 of the section, and wdiich contain, in addition, pebbles of the under- 

 lying Heuvelton. These relations indicate an erosional uncon- 

 formity between the two formations. And this would naturally be 

 expected since, farther east, the Tribes Hill formation wedges in 

 between the two, with indication of a break between it and the 

 Ogdensburg. The so-called upper Heuvelton here consists of a 

 three or four foot thickness of thin-bedded, sandy dolomite which 

 may possibly be itself of Tribes Hill age. No fossils were seen in 

 it and the reference is uncertain. If really Tribes Hill it is but a 

 trifling wedge of the formation, and the break indicated by the 

 exposures is the one between the Tribes Hill and the Ogdensburg, 

 rather than one at the summit of the Heuvelton. 



These first exposures of the Ogdensburg formation are about 

 4 miles northeast of Morristown. Following along to the east no 

 exposures appear within the next mile, owing to a thin, morainic 

 covering, after which they reappear and, except for occasional 

 short gaps, continue all the way to Ogdensburg. The first outcrops, 

 north of the road, show a thickness of 16 feet of the basal beds 



