Its NEW YORK STATE MUSEUM 



cause of the subsidence was the removal of a barrier at the south 

 which held in the waters or to regional uplift. 



The Lake Albany deposits comprise (i) the mass of stratified 

 clays and sands whose surface forms the terraced slopes of the 

 Hudson valley and (2) the sands and gravels of tlie Hoosic delta. 



The clay and sand formation, as already stated, forms the filling 

 of the ancient rock valley of the Hudson. The lower beds of the 

 formation consist predominantly of clay and are the source of the 

 well-known brick clays of the upper Hudson region. As seen in 

 the pits at the brick-making plants, the clays are fine grained, 

 evenly laminated and of a bluish color below passing to yellowish 

 above. As exposed in mass at the slopes fronting the river valley 

 or along the ravines, the weathered surfaces are of a buff or 

 yellowish color. The compact clays make up perhaps the lower 

 100 feet of the formation, above which they grade into sand, clays 

 or clayey sands. The latter, in certain localities (as i mile south- 

 west of Mechanicville) have the composition requisite for mold- 

 ing sands. 



Farther back from the river the materials of the Lake Albany- 

 deposits are coarser and consist more largely of sands. In places, 

 however, the clay constituent still predominates and there are 

 tracts of considerable extent at or near the 300-foot level, as west 

 of Melrose, where the lands are of clayey character. 



The surface of the clay and sand formations is marked by strik- 

 ing topographic features. These are (i) the terraces of which an 

 upper and a lower are distinguished and (2) the ravines which 

 cross the terraces, dividing them, especially the lower one, into 

 segments. 



The upper terrace is less well defined than the lower. In places 

 (as west of Cohoes and southwest of IMechanicville) it appears as 

 a nearly level expanse, one-half of a mile or more in breadth, 

 bordered at its outward side by a slope toward the uplands and at 

 its side toward the river by a more gradual slope to the level of the 

 lower terrace. This description applies generally also to the upper 

 terrace on the east side of the valley as it appears north of Crandall 

 Corners and northwest of Melrose. In other places (as west of 

 Stillwater) the upper terrace is less perfectly expressed, being 

 narrower and with surface falling toward the river. In places, 

 also, as at the Saratoga battlefield, the level of the terrace is broken 

 by hills of till (or till-covered rock hills) which rise above the 

 lacustrine deposits. East of Lansingburg the upper terrace (as also 

 the lower) disappears as a distinct form feature, the steep rock 



