6:54 NEW YORK STATE MTSEUM 



\n^ content of the gravels ; uiid, 2) the erosion of valleys and 

 liarhors in its mass prior to at least the last till deposits on the 

 island. The latter phenomena are so extensive as to indicate a con- 

 siderahle lapse of time for their production. 



Discoloration of the gravels hy the yellow or hydrous sesquioxid 

 of iron has taken place to a variable extent, sometimes affecting less 

 than a cubic foot of the materials and in other places, particularly 

 beneaih the moraine, changing the entire appearance of the section 

 there exjKjsed. 



I^)cal discoloring by the yellow oxid is frequently seen in the 

 gravel pits on the west shore of Hempstead bay, wherever some 

 iron-bearing pebble has oxidized and.hydrated, the iron salts spread- 

 ing outward and mainly downward through the action of infiltrating 

 rain water. The sands and gravels above the till bed mainly exhibit 

 this change. 



Widopread discoloration of the gravels to a deep yellow occurs 

 in Koslyn in the bluffs on the east side of the town below the base 

 of the momine. This deeper and more thorough coating of the 

 gravels in this locality is a natural result of the lixiviation of the 

 ferruginous rocks in the overlying moraine, the products of whose 

 oxidation and hydration have worked downward into the porous 

 gravels beneath. 



The di.scoloration is therefore a change which is probably secular 

 and in progress. That it had already advanced very far before the 

 moraines were formed is indicated by the abundant occurrence in 

 tiie moraine of yellow, stained quartz pebbles ; but these pebbles in 

 the moraine are usually not in the place in which they were originally 

 stained, for thev have water-washed surfaces. The staining: was 

 accomplished while the pebbles lay in an earlier deposit, either the 

 Columbia or some unexposed member of the ancient coastal plain. 



Erosion interval. The evidence of late dislocation on a small 

 scale commensurate with the pushing and dragging action of a 

 great ice sheet, the spreading of till and boulders over the surface 

 of the Columbia, and the amassment of heaps of drift evidently in 

 part derived from the surface of the deposit, afford indubitable evi- 

 dence of the degradation of the formation to some extent by ice 

 action subsequent to the completion of the series of deposits. But 



