GLACIAL AND POST-GLACIAL HISTORY 445 



ing to a point three-quarters of a mile north of that place. For a 

 half mile at its southern end it borders the undulatory gravel area 

 mentioned above in connection with the 100-120- foot terrace. Nearer 

 its north end it is separated from a higher deposit of sand-capped 

 clay by a till area which has a shghtly undulatory topography. (Fig. 

 5, D.) Opposite this low terrace, at Roseton and north toward 

 Danskammer Light, a gravel-capped clay deposit occurs at a slightly 

 higher level, with a terrace form. There are two hypotheses to 

 explain these relations: (i) The deposits at Roseton once extended 

 entirely across the valley and have since been eroded, and the 20-40- 

 foot terrace is the product of erosion of the higher deposits. (2) The 

 second hypothesis is that the Roseton gravel-capped clay terrace 

 and the high-level clay deposit on the east side of the Hudson were 

 never continuous, but that the ice occupied the valley when they 

 were made, and stood on the 20-40-foot gravel terrace, but failed 

 to build it as high as the 100-120- foot terrace to the south, or the 

 Roseton terrace to the west and the clay to the east. The sinks in 

 the 20-40-foot terrace, and the faint undulations in the till on he 

 slope between the 20-40-foot terrace and the higher clay, bear this 

 out. If this is the correct interpretation, it is a case similar in kind 

 to the kame-like knolls near the North Haverstraw gravel plateau, 

 and also like the phenomena just south of Peekskill near Verplancks. 

 Under this interpretation the 20-40-foot terrace may or may not once 

 have extended entirely across the valley. Under the first hypothesis 

 both the high-level and the low-level terraces formerly extended 

 entirely across the valley. It may be objected to the second hypothe- 

 sis that when the ice had retired to New Hamburg, and the clays 

 and sands and gravels were accumulating, some of the finer mate- 

 rials at least should have been carried south into this unoccupied 

 part of the valley. This argument would be especially strong if the 

 Hudson water body was subject to tides whose ebb would tend to 

 carry the fine detritus down into this space. It is, however, not at 

 all necessary to beheve that the valley between these two terraces 

 was unoccupied at this time. If the valley was occupied, it was by a 

 mass of stagnant ice. There is evidence elsewhere that such masses 

 of stagnant ice were left in the valley. 



