636 PROCEEDINGS OP THE BALTIMORE MEETING 



Leyden quadrangle the Paleozoic rocks are distinctly terraced. The steep 

 front of the lowermost terrace rises from 200 to 300 feet, and immediately 

 faces the river. The basal sediments here are weak sandstones and sandy 

 limestones, while the surface of the terrace (several miles broad) is made up 

 of hard Trenton limestone. Along the western edge of this terrace a second 

 slope (Tug hill) rises over 400 feet within a third of a mile. The base of this 

 slope is made up of the soft Utica shale, while the upper part is made up of 

 the Lorraine sandstone and shale. 



The steep fronts of the terraces are certainly young topographic features, 

 which preclude the possibility of their having been formed during the long 

 pre-Glacial period of erosion in this very ancient region. On the other hand, 

 little work of erosion has been done in post-Glacial times, as proved by the 

 fact that Black river has not yet cut its way through the recent deposit filling 

 the valley bottom, and also because striae and kames near the river level have 

 not been disturbed. There is still the possibility that glacial waters might 

 have developed the terraces, but there is no evidence for any such vigorous 

 water action, especially along the higher part of the limestone terrace, where 

 records would surely be left. Kames and glacial strise are here left undis- 

 turbed. Evidently the lowest sediments were cut back by the ice to' develop 

 the steep slope which now faces Black river. As Robert Bell has suggested for 

 certain Canadian occurrences, 3 the exposed edges of the sediments resting 'on 

 the very hard pre-Cambrians presented the most favorable attitude for ice ero- 

 sion, and they were stripped off the pre-Cambrians until, as Bell says, "the 

 resisting rock front had attained a height and weight sufficient to counter- 

 balance those of the glacier." In much the same way the steep front of the 

 second terrace was developed by stripping off the soft shales from the hard 

 limestones. The maximum amount of shale thus removed was probably sev- 

 eral hundred feet, but not over a wide area. Ice erosion was considerably 

 favored by the fact that the ice moved uphill along the valley, and so had its 

 cutting power increased. Another factor of importance was the angle at which 

 the ice current entered the Black River valley in its sweep around the Adiron- 

 dacks. The greatest amount of erosion was along the eastern side of Tug hill, 

 and it was just here where the ice must have struck with greatest force as it 

 crowded into the valley. 



A remarkable development of glacial sand plains or terraces is to be found 

 within the region here discussed. The greatest sand plain expanse extends 

 from Forestport to an unknown distance north of Lowville, and it has a width 

 of from 5 to 8 miles. This great sand plain has a rather steep front facing 

 Black river, where the deposit is from 200 to 250 feet deep, while it thins out 

 to disappearance eastward. The remarkably concordant altitudes of the plains 

 (from 1,150 to 1,260 feet) ; their crudely stratified character; the general ab- 

 sence of erratics over the surfaces, and their frequently lobate character all 

 argue conclusively for their origin as delta deposits which were formed in a 

 marginal lake along the waning ice during its retreat from the higher to the 

 lower land along the western Adirondacks. Another fine but smaller sand 

 plain covers about fifty square miles between West Canada and Black creeks 

 (Remsen sheet). A thick bed of clay underlies this sand, and the sand was 



» Bulletin of the Geological Society of America, vol. 1, 1890, p. 296. 



