ARTESIAN WELL SECTIONS AT ITHACA, N. V. 77 



upper portion of this lower series of coarse materials; (4) the 

 marked variety of materials" composing the lower series, which 

 vary from gravel and sand to till, thus closely resembling the 

 moraine that rises to the surface farther south ; (5) the large per- 

 centage of water-washed material, again resembling the condition 

 in the moraine farther south. This large amount of water- 

 washed material would be expected where the ice-front stood in 

 a deep lake, as was the case here. 



Glacial lake clay. — It is well established by the evidence of 

 various overflow channels, by well-defined elevated deltas at 

 various levels,^ and by lake clays on the hill slopes, that the 

 Cayuga Valley was occupied by a steadily expanding, ice-dammed 

 lake, with its level frequently lowered as successively lower out- 

 lets were discovered by the melting back of the receding ice- 

 sheet. This lake condition lasted for a long time; in fact, until 

 the Mohawk outflow was discovered. The length of this period 

 of lake stage cannot be stated ; but it was sufficient for the ice to 

 have melted back at least forty miles. Of necessity a great 

 amount of clay must have been deposited in this lake, not 

 merely that supplied from the glacier, but that washed from the 

 hill slopes, and that brought by the streams which descended the 

 steep hill slopes. 



The great thickness of clay found in all the wells, usually 

 between the 100 and 200-foot levels, is interpreted as lake clay 

 deposited in this ice-dammed lake. The great thickness of the 

 clay stratum, its uniform character, its occurrence in all the 

 wells, the general absence of animal remains and the presence of 

 only minute fragments of plants, the occurrence of scratched 

 pebbles that might have been ice-borne, and the increasing 

 coarseness of the clay toward the bottom, all harmonize with 

 this interpretation. No opposing facts were discovered. 



Recent lake clays. — The uppermost clay beds, between the o and 

 40-50-foot levels, with abundant organic remains and an almost 

 complete absence of sand and pebbles, are interpreted as lake 



' See papers by Fairchild, Bulletin Geological Society of America, Vol. VI (1895), 

 PP- 353~74 ; Vol. X (1899), pp. 27-68; and by Watson, A^ezv York State Mtisewn 

 Report j I (1897), Part I, r 55-r 117. 



