52 WILLIAMS— DEEP KANSAN PONDINGS IN 



stagnation in the pocket, and a high ice-dam as its cause. The 

 gravels are found along the Rondout-Wallkill Valley, and indicate a 

 current of 30 inches per second passing thence from the Hudson, 

 and a depth of water — 314 to 514 feet — sufficient to pass over its 

 saddle. 



Both clay and gravel are sorts of a glacial outwash. The clean- 

 ness of the former indicates a recession of the glacial front to the 

 north sufficient to permit the separation of the sand and gravel sorts 

 from the clay as soon as a slackening of the torrential current oc- 

 curred. The volume of the torrent can be inferred from the fact 

 that the Hudson Valley drained that part of the St. Lawrence basin 

 which passed through Lake Champlain — all from the glacier and the 

 region between the Green Mountain-Taconic range on the east and 

 the Delaware-Susquehanna watershed on the west, and all from 

 Central New York that did not escape south or west. Such a flood 

 would clear away at once whatever deposits in the Hudson Valley 

 were within the area of scour, as soon as the ice-dam in the pocket 

 became weak. 



This episode is an archetype of our periodic freshets, with their 

 high water, their thin washes of slimes and of light trash, and their 

 rapid subsidence. Nobody associates the distance between the high 

 levels reached by the slimes, and the midsummer low water, to 

 which they run continuously, as indicating the depth of excavation 

 in a completely slime-filled valley. Nor do we so theorize about 

 sporadic gravels dropped in deep pondings, such as will now be con- 

 sidered. 



Delaware Narrows Ponding. 



A similar ice-dam was formed south of Easton, Penna., in the 

 Delaware Narrows, of bergs from the Hudson, and from the glacial 

 lobe which crossed the former river north of Pocono Mountain. It 

 ponded the Lehigh Valley up to 500 feet^ during the wasting of the 

 Hudson-Delaware-Schuylkill lobe there. As evidence of Arctic in- 

 trusion we find Sedum rhodiola growing on the side of the narrows 

 where the sun never intrudes. This and Quoddy Head, Maine, are 

 the two habitats of this plant in the United States. 



The deposits in this ponding are sporadic. The most prominent 



